The young girls slip long dresses of fuchsia and aquamarine over T-shirts and shorts, swishing and swirling them in time to the beat. The teenage boys, solemn in concentration, join in, stepping and stamping, hands clasped behind their backs.

They are clearly having fun, but they and their parents are clear this is not just about keeping them amused. It is about nourishing their Mexican roots, making sure their culture doesn't shrivel and die in this corner of the Deep South.

I have come to Springdale because it is a harbinger of America's future. Ten years ago there were hardly any Latinos here - now they make up more than 30% of the population. Predictions suggest that by 2030, that is what the US will look like.

Right now, one in four Americans under 18 is Hispanic - that is, Spanish speakers with roots in Latin America. A lot has been written about the political impact of the growing Latino population, but I am interested in how it could change the culture, indeed the very nature, of the United States itself.

"The richness of our culture is not just music and dance, but who we are," Margarita Solorcano, the director of the dance project, tells me.

"Living here, we have a lot to learn, but we also have a lot to teach, like the family unit, the sense of community, the loyalty to our traditions."

She says they have already altered attitudes in this very traditional and very white part of the world

"I feel it is changing - we are here, and everybody is learning from each other," she says.

"In the Deep South there are people who haven't had the experience of being around other types of people, so when they start mingling with different cultures, their attitudes change."

Of course, some parts of the US have always felt very Hispanic. Large swathes of the South-west were still part of Mexico until the 1860s - just a heartbeat ago in historical terms.

As one young woman in Texas told me recently: "People ask when my relatives came across the border.

"I tell them, the border came across my ancestors."

What is different now is the huge growth in the Latino population far away from the border, sometimes in areas without a tradition of immigration from anywhere but Europe.

One of the dancers, Myra Rivas, suggests the growing Latino population defines one vision of what America should be.

"It will make a huge change," she says. "America is more than just America."

"Without Hispanics, without all these other cultures, it isn't really America. The US provides opportunities to every single culture there is and that's what makes America different."

When I ask what Latinos specifically bring to the US, she giggles and says: "The food! And our good looks!" The other dancers agree the food is pretty important.

While some Hispanics are wary of this stereotype, it is what many Americans think.

According to one survey around 80% think Latino culture has had a large influence on the US, and most say the biggest impact is on food and music.

It's true that tacos are as American as curry is British.

But perhaps Latinos add more than just a little spice to American life.

I go to Springdale's St Raphael's Catholic Church in search of a more profound answers. The airy church is framed by two large modern stained-glass windows. Father John Connell is saying Mass in Spanish.

It is one of three mid-week Masses in the language, which he learnt five years ago. After the service he tells me the increase in the Latino population has made a big difference, especially in his diocese, which covers the whole state.

"It has meant a huge change," Father Connell says. "We are pushing close to 200,000 Catholics in a diocese that used to have around 60,000.

"In the United States our Latino brothers and sisters are a blessing to the church. Without them the church would have been stagnant in numbers."

And he's sure it will grow still more.

"Almost every Latino woman in my parish is pregnant, so they are still in that mode of mother, family, father, three, four, five, six kids. So what's the impact? A huge explosion of Latino babies in the years ahead."

I ask him if a growth in Catholics means America will become more socially conservative. He's wary of that conclusion.

"I agree it may have some type of impact," he says. "Latinos come from predominantly Catholic countries, and their culture and religion are all wrapped up in one.

"We in the United States individualise everything - politics, religion, culture - it is all separate. Will it change? I don't know.

"The second generation will speak English, the third generation, they may not even speak Spanish and they may forget a lot of traditions and culture of their parents. That's the history of any immigrants to this country."

That's true. But this might be different for Latinos, for a couple of reasons. First of all, the Spanish language is already ubiquitous in the United States, and there are areas of the country where you need speak no English.

There are the big TV networks for a Spanish-speaking audience, Telemundo and Univision, as well as many newspapers and radio stations.

Many public notices, for instance on the buses I take in Washington DC, are all in English and Spanish.

Some schools are bilingual and those irritating automatic telephone options nearly always ask you to press one for English, two for Spanish.

All of this is constantly reinforced by new waves of Spanish-speaking immigrants who may have little English.

At Springdale Har-Ber High School, I sit in on a class for teenagers who are new to America. They are learning English through American history.

"What was the New Deal? Is it a he or a she? No it's an 'it'!"

The animated teacher, Jana McVay, engages the kids, putting her finger to her lips, acting out puzzlement, asking the kids questions.

She says it is important her pupils learn English.

"It's essential if they want to be successful," Ms McVay says. "I want my students to have the American Dream. I don't want my students to think they have to work in a factory.

"If they want to get a management job, go to university, they need to speak English."

But she doesn't think that means they have to lose Spanish, or their culture.

Perhaps becoming American no longer requires subscribing to a narrow vision of what that means.

"I have a friend who is a Latina and she can't speak a lick of Spanish - her parents subscribed to the idea that you come here and you become a Wasp," Ms McVay says.

"But that is changing and I think it will change the country. We talk to the kids here and they have an identity and they need not try to become someone else.

"They are aware that there is no box to fit into. The country is changing, it is becoming what it is, because of who they are."

Brenda and Carlos, two 16-year-old students from Mexico, can't imagine ever feeling American, but understand the lure.

Rick Schaeffer, communications director of Springdale public schools, says this corner of Arkansas is definitely a taste of what is around the corner for the country. And while some around here wouldn't agree, he thinks it is positive.

"America has always been a nation of immigrants, ever since the 1700s," Mr Schaeffer says.

"If you look at the Hispanic culture, they might be more like Americans used to be than Americans are today.

"They are family orientated. You don't see divorce. You sure don't see abortion. They are hard workers. They are industrious.

"In a way, they are a lot like the immigrants who came here in the 1700s, who built our great country into what it is today."

All those I spoke to were positive about what the increase in the Latino population would mean - although I didn't specifically seek out critics.

But I came away with a strong sense of one vision of America - that it is a project still in motion, and that the more it mirrors the world, rather than reflects a European identity that others have to squeeze into, the stronger it is.

Look at the words he's used: "outrageous", "intolerable", "inexcusable", and if you didn't get it, "wrong".

Meanwhile, Treasury Secretary Jack Lew is "deeply troubled" and has "zero tolerance" for behaviour that is "inappropriate" and "unacceptable".

They are right to come out hard and fast. For one arm of the government to target its most vociferous opponents is the sort of thing that happens in dodgy banana republics and failing democracies.

Although the IRS commissioner has denied any staff acted out of partisan motives, political critics are doubtful.

This, and the raid on the AP, will confirm the belief of Mr Obama's opponents that this is an overweening administration dedicated to trampling on the freedoms of the American people. Whatever language the president uses, they will believe that somehow he was behind it.

His political enemies are turning up the heat. I have already received one email from a Tea Party group, using it to drum up campaign funds. One senator has compared Mr Obama to disgraced former President Richard Nixon, and claimed the rot starts at the top. He won't be the last.

It is explosive ordnance for his enemies. The reason he has had to be so firm, so quick, is that if he allows it to fester, as he has with scandals in the past, it will seep into the general public imagination, and seriously harm his administration's image.

He has to establish, from the top down, to Democrats as well as others, that this is not an occasion to score party points - it is a national scandal which needs to be roundly condemned by everyone.

That may mean some of the worst odour slides off. But mud does stick. It is a bad week for the president.

It is true that plenty of groups claim to be non-political when most sensible people would say that politics is their main purpose. But on the evidence so far, it seems only right-wing groups were targeted - and more bizarrely still only small local ones, not the huge lobby groups.

This affair, along with the justice department's raid on the Associated Press, is likely to have a political impact. Conservative groups have long claimed an overbearing administration is targeting their freedoms and that abuses of power are ignored by a complacent media. The events of this week will strengthen their belief that someone is out to get them.

The purpose was the desire of the British and American media to get under the skin of their leaders, and ask awkward questions. But they were interested in completely different stories.

Given that each country's journalists were only granted one question apiece it was a tribute to their deployment of the multi-warhead portmanteau question that they actually got answers on everything that mattered.

For the American press it was Mr Obama's take on the Internal Revenue Service's (IRS) apparent persecution of the Tea Party movement that was most interesting.

He obliged while hedging his bets a bit. He said if it had happened, it was "outrageous", against all the traditions of impartiality.

On Benghazi he was a good deal more feisty, even fed up. He suggested the continuing accusations of a cover-up were politically motivated, defied logic, and dishonoured those who serve the US abroad.

The whole tale has become so highly hyper-partisan, with some denying there was any hanky panky at all around the briefing notes, and others concocting a tottering, towering conspiracy, that it is hard to find anyone in the US media seeking the rational kernel of truth - but this New York Times article does a good job.

David Cameron was pursued by the Conservative Party's familiar family ghost - questions of the UK's relationship with the EU.

President Obama came to his aid, suggesting that Britain's place as an "active, robust and engaged" country meant it should be in the European Union.

He then stuck his neck out further, arguing Mr Cameron was right to attempt to fix an apparently broken relationship before breaking the whole thing off. The president is a better friend to the prime minister than some party colleagues.

The US genuinely would be alarmed if Britain really did exit the EU stage right, but at this point this was more about helping a pal than ringing alarm bells.

Then there was Syria, which will not make many headlines, but probably was a main focus of the talks themselves.

Mr Cameron came across as more eager, stressing the urgency of the situation and the worth of the Russian peace talks.

The difference in tone is probably because Mr Cameron is more of an enthusiastic liberal interventionist than his ally, who is adverse to overt US engagement in the Middle East and sees Syria as difficult and dangerous to fix.

They both said they and the Russians wanted the same thing - a stable Syria without extremism. They did not add that the Russians think that was the situation two years ago.

Conventional wisdom is that all senior politicians end up turning their attention to foreign affairs because at least they can do something, whereas the domestic agenda is insoluble.

It is a testimony to the intractability of the Syrian conflict that even innuendo over the IRS and the Tory civil war seem attractive by comparison.

The UK prime minister is in the US partly for a big meeting at the UN on global development and partly for an event with Prince Harry, also in New York.

So his meeting with the president is something added on, rather than the centrepiece of his trip. That means it will be strictly business - no playing of ping pong or sampling of BBQ. As well as Syria, they will talk about Iran, transatlantic trade (the proposed deal with the EU is now known in the trade as "tee tip") and probably North Korea.

Doubtless the president will want to know the latest about the prime minister's proposed referendum on membership of the European Union and his troublesome colleagues' willingness to turn a political face-saver into a real choice. While some in Britain dream of leaving the EU and strengthening the transatlantic relationship it its place, America values what the president calls the "essential relationship" in part as a bridge to Europe. If it turns into a bridge to nowhere, it will trouble them.

But Syria is the hard case. Both Europe and the US are slowly inching towards arming the rebels. But that commonplace phrase disguises the fact that the "arms" will be well short of anything the rebels actually want to finish this protracted business.

For months now, the noises from Western capitals have vacillated between the cry "Something must be done!" and the forlorn reply "But what?"

One rather lame answer is the idea of a peace conference dangled by Russia.

But there's not much diplomatic chatter about the proposal, which seems more like a passing thought than a hard plan. I get the impression that the US and Europe will go along with what they privately regard as a bit of a charade only because they have no better ideas.

Which brings us back to "arming the rebels" and allied concepts like a no-fly zone.

Enthusiasts insist it isn't that difficult - find the right sort of rebels and give them the weapons they need. But as one insider put it to me: "What if we give the minority we trust the good stuff and five miles down the road they run into a road block and Islamist nutters take it off them? How does that help?"

No-one has any particularly good answers to this conundrum. We'll see today if the two leaders can come up with anything that squares the circle.

The other reason given - old-fashioned butt-guarding - is more credible. However you read the motives, the state department and apparently the White House did get the CIA to change its story.

This is now very serious, and I suspect heads will roll. The White House will be on the defensive for a while.

Conservatives have long maintained that the administration deliberately suppressed the truth about the attacks.

This is the first hard evidence that the state department did ask for changes to the CIA's original assessment.

Specifically, they wanted references to previous warnings deleted and this sentence removed: "We do know that Islamic extremists with ties to al-Qa'ida participated in the attack."

There's little doubt in my mind that this will haunt Hillary Clinton if she decides to run for president, unless she executes some pretty fancy footwork.

State department spokesperson Victoria Nuland is directly implicated, and the fingerprints of senior White House aides Ben Rhodes and Jay Carney are there as well.

In the interests of full disclosure I have to say I have not in the past been persuaded that allegations of a cover-up were a big deal. It seemed to me a partisan attack based on very little.

I remember listening to reports from the BBC and others at the time that did suggest the attack in Benghazi was a spontaneous reaction to a rather puerile anti-Islamic video.

I understand President Barack Obama's careful use of the word "terrorism" when it actually means something, rather than as a knee-jerk description of any violence by foreigners against Americans, often in order to justify a "war on terror".

But the evidence is there in black and white, unless we doubt the documents obtained by ABC, which I don't.

Mr Obama's critics are often not very clear what is behind their allegations. I presume they think that the White House wanted to avoid claims the murders were the result of terrorism because this would undermine his claim that al-Qaeda was seriously "degraded". There's also a vague sense he's "soft on terror".

The new documents contain two rationales for the changes in language. The first is that it would prejudice the FBI investigation.

Perhaps, but I am not at all persuaded.

The other reason given, old-fashioned butt-guarding, is more credible.

As Ms Nuland puts it, such a report "could be abused by members [of Congress] to beat up the State Department for not paying attention to warnings, so why would we want to feed that either?"

However you read the motives, the state department and apparently the White House did get the CIA to change its story.

This is now very serious, and I suspect heads will roll. The White House will be on the defensive for a while.

The B-52 bomber is one of the ultimate expressions of American power. If the president decides to drop a nuclear bomb, this is the sort of aircraft that would do it.

I am careful not to step over the red line around the plane. A sign painted on the ground warns lethal force can be used against those who cross it without authorisation.

I've come to Minot Air Force Base in North Dakota, filming for the new BBC One programme The Editors.

The programme aims to get the BBC's on-air editors to explore - and hopefully answer - a big question. My chosen subject is the decline of American power.

There's little evidence of it at the base, where the sign above the gate reads: "Only the best come North".

An old Minute Man missile stands to one side of the entrance.

The road names here are a testimony to the base's purpose - Ballistic Avenue and Cruise Missile Lane. It is home to two arms of America's nuclear strike force, the Fifth Bomb Wing - known as the Warbirds - and the 91st missile wing, the Rough Riders.

As I talk to a group of very normal, bright and cheerful men and women from both units, I am awed by the potential nature of their job.

I joke that when things are really stressful and going very wrong, some people in my business say: "It's only television." They can hardly say: "It's only nuclear war."

As well as confidence in their routine and their abilities, they have faith in the nature of American power. They all stress that their job is deterrence. They hope these weapons will never be used.

But I put it to Capt Kim Brown that she would be the one to pull the lever, to drop the bomb.

"As the offence team we are responsible for weapons activity... dropping the right type of weapon on the right type of target," she says.

"That's quite a responsibility," I say.

"It is," she replies. "But it's what my nation asks me to do. It's my job, and I trust those above me that they are well-informed to make those decisions."

I ask Capt Chris Duff about the responsibility.

"It is one I embrace. It is what I signed up to do," he says. "If it is called upon I will do it."

He is confident America acts for good in the world.

"The US obviously spreads democracy throughout the world, it's been proven to do that," he says.

"We are still a good Christian country. I am a Christian and it is founded on Christian morals. I have faith in the president and all my leadership."

Capt Duff was born in Liverpool and his parents were English. He chose to become an American. Does he think his adopted home is as great as it once was?

"I'd say yes," he answers. "This jet has been around for 50 years. It is still capable of reaching out and touching anyone in the world at anytime, should the need arise."

Not everyone back east is so confident. In the four years I have been based in Washington DC, there have been a flood of books and articles on the decline of American power.

Perhaps Americans fretting about their place in the world is nothing new. There was the "Sputnik moment" in 1957 when the US thought there was firm evidence that it was being out-stripped by the Soviet Union. There was the fear of Japanese economic dominance in the 1980s.

Watch Mark Mardell's report from North Dakota as part of an episode of The Editors presented from Washington on BBC1 at 23:25 BST on Monday

More from the programme

My colleague Kim Ghattas, in her book The Secretary, highlights this quote from Charles Dickens's Martin Chuzzlewit.

"Martin knew nothing about America, or he would have known perfectly well that if its individual citizens, to a man, are to be believed, it always IS depressed, and always IS stagnated, and always IS at an alarming crisis, and never was otherwise; though as a body they are ready to make oath upon the Evangelists at any hour of the day or night, that it is the most thriving and prosperous of all countries on the habitable globe."

But this time it is different. There can be no doubt America is in relative decline. Its economic and diplomatic power are not what they were. And there is no doubt it bothers many Americans.

For a while, everything was bigger in America - from skyscrapers to the sky, from the dream to the nightmares. The manifest destiny of expansion to the West perhaps gave rise to the illusion the horizon was endless.

But there are others with new frontiers now, and America's world is shrinking. The biggest economy in the world now has the biggest debt in the world.

This plays into an odd insecurity - in a country famously ignorant about abroad there is a curious stress on the very word America: American idols, American heroes, American dreams.

For it is a young country, still creating itself, reassuring itself that it is special, indispensible. Those who are aware of it may be hurt that they are not loved - and that hurt is most easily assuaged with bombast and swagger.

Belief in the notion of decline can be encouraged by both political parties, even as they trumpet America's superiority.

The Democrats believe America is falling behind in economic terms because of a refusal to invest in the infrastructure - and it really is crumbling; in some places it feels more like the developing world than Europe.

They would launch a taxpayer-funded crusade against decline, against poor education, a drive to create more talented graduates and invest in the technology of the future. That is one vision.

The Republicans' case is perhaps more interesting, more romantic, and more specifically American, although not necessary more true.

They warn America is growing away from its constitutional roots, doomed to decline by debt and outsized government.

In this vision, it can only save itself by being true to its destiny. It must want to be not only a power, but the power in the world, assertive, a leader, and if necessary a warrior nation once more.

But in large measure, the reality of decline that it is part of a huge historical re-balancing act - something we acknowledge in words like "globalisation" or "Brics", while often ducking just how profoundly the world is changing.

The model we in the West grew up with - and our great-grandfather's parents grew up with too - turns out not to be immutable.

Remember, wealth and power were pretty evenly distributed in the world until around the 16th Century. The rise of the British and other European empires, with their technological and ultimately military superiority, threw the world out of joint.

The US was heir to that, with the added power and zest of its expansion. In two world wars American intervention was decisive. Without its political commitment much of Europe would have been behind the Iron Curtain, and arguably the Cold War would have been lost.

At the same time a dream was coming true in the US: prosperity that spread to a huge middle class.

It is important not to be too rosy-eyed about this; poverty and discrimination were also present on a monumental scale. But it led many Americans to see themselves as the end product of Western democracy.

Perhaps they were.

Now the world is rebalancing - power and wealth will become more evenly distributed across countries. So yes, China will rival the US, and so will others.

But let no-one mistake how far above the rest of the world the US has risen.

It would take a lot - a catastrophic event - to dent the most powerful military the world has ever known - especially when the US spends more on its military than the next 12 big spenders. That's more than China, Russia, the UK, Japan, France, Saudi Arabia, India, Germany, Italy, South Korea and Australia added together.

It takes time for that sort of power to erode.

But military might does not stand alone. China's Chairman Mao said that power grows from the barrel of a gun, but guns cost money - power perhaps grows from a fistful of dollars.

And the American economy too has felt severe shocks recently. It will probably not remain the biggest economy in the world - some predict China will overtake it in three years' time.

I drive on, through the land that was the Old Wild West.

I am sure that it was in part that sense of spreading across a huge continent, the possibility of seemingly endless expansion, that gave America the feeling that there were always new frontiers to conquer.

Perhaps the daunting climate and the constant attacks by those who originally lived on this land heightened a sense that the world was a hostile place that had be wrestled into submission, that justice was rough or not at all, that violence was the answer, that when the chips came down you were on your own as well.

Now horizons and old certainties are shrinking.

But much of North Dakota is still empty, and it still feels like the barrens.

Williston seems like a gold-rush town. It is the base for the exploration of the Bakken oil field, the biggest in the US. It has been made possible because of developments in fracking - the technology that uses pressurised water to pulverise the rocks and force them to yield their treasure of oil and gas.

The town has quadrupled in size recently. After travelling for hours on nearly empty roads it is a shock to be hemmed in by huge trucks thundering past on every side.

Everywhere signs flash "For hire". Ramshackle buildings look as if they have sprung up overnight, offering BBQ or a place to stay.

Local legend says it cost more to rent a house here than it does in Manhattan. The state has the lowest unemployment in America.

"If you can't find a job here there's something wrong with you," a truck driver tells me, sitting high in his cab about to deliver the special liquid that drives the fracking process.

On the edge of town there are "man camps". They have been formally renamed "crew camps" in the interests of equality, but the new name hasn't stuck.

Hastily constructed to house all the transient workers, they don't feel like Dodge. They are rather nice, spotlessly clean with neat rooms like student dorms. But they are testimony to the fact there is money to be made here.

The source of this newfound wealth is celebrated in the jewellers on Main Street. The window is full of pen holders, desk clocks and ornaments, in gold, all in the shape of oil derricks.

Fracking is hugely controversial, both for its impact on the local environment and CO2 emissions. But it is here to stay, and it makes a real difference to America's future.

The projections are that the US will be energy independent by 2020. All that cheap energy is already having an impact, one of the factors behind the return of industry to the country.

Standing next to huge "nodding donkeys" that suck the oil from the earth, I talk to Kathy Neset, who has worked in the industry since the 1980s as a consultant. She's a geologist by training.

"These wells right here are producing something like 800 to 1,000 barrels a day, for each one," she tells me.

"That oil is about two miles under our feet and I anticipate it will last for another 20 to 30 years. That is our energy security. "

She thinks this is evidence of America's future:

"I think our country is going up, up, up. The potential is shown right here in North Dakota."

But hasn't America, like the British Empire, like the Greeks, had its day?

"America's day is still coming," she insists. "We are on the upswing. And this is a perfect example of how American ingenuity is taking us on to the next frontier."

"We continue to reinvent ourselves... We have a new frontier, this oilfield, but we would be very short-sighted if we said this is the best we can do. There are more frontiers."

There will be many Americans who agree that their country has an endless appetite to pick itself up, dust itself down and reinvent itself.

At the end of my journey I find myself unable to give a straightforward "yes" or "no", as the programme would like.

Instead I have a series of reflections on the decline of America.

There can be no doubt the "rise of the rest" will make America shake on its pedestal, but whether it knocks it off is up to Americans themselves, and whether they can adapt to a new status, a somewhat lower place on the greasy pole of world power.

The colossus will no longer effortlessly bestride the world; that does not mean it will not stand tall.

They should not underestimate the importance of soft power. All over the world granddads and infants, jihadists and dictators, wear jeans, America's off-duty dress of choice.

That may sound trite, but the fact the world increasingly looks like America is important. Rock and rap, the English language and Hollywood and still dominate popular culture.

Those defenders of America who attack knee-jerk anti-Americanism are rather missing the point. Those all over the world who might say they are anti-American don't hate Jimi Hendrix and Woodie Guthrie, Levis and denim, Andy Warhol and Jack Kerouac.

They don't, usually, hate freedom or democracy, but a certain cynical exercise of America power sheltering behind those values.

It is important to remember America is still a very young country, with very bright dreams. It's a teenager, admiring its muscles, throwing tantrums, amazed and scared by the wider world.

It is still wondering what it will be when it grows up, still hoping for greatness. But uncertain of its identify, asking itself profound questions about the way it is changing.

Is it a melting pot of immigrants from many lands, some unwilling, where Korean and black and Hispanic culture is celebrated every bit as an English or German heritage?

Or should newcomers, bring no more than a few folk songs from their old home, and squeeze into a white Anglo-Saxon Protestant definition of what it is to be American?

Should America lead the world, from the front, not frightened to right perceived wrongs all over the globe? Or should it, as President Obama wants, be cautious in the exercise of power, sensitive to the feelings of others, willing the right thing, not demanding it?

Then there is the time scale.

Decline can be a long time coming and soft power can echo down the centuries. But often greatness does not endure.

We have all but forgotten the Medes. Carthage is unmourned. And who has heard of the Aksum empire?

But then there is Rome.

By around 40 AD a canny Roman might have predicted the Empire's decline. But it took another 400 years to fall, and it was more than another 1,000 years beyond that before another empire grew as mighty.

In 2,000 years could English be a dead language, used only in liturgy, but still studied in schools? More importantly will American values, often honoured in the breach nowadays, have transformed the world into a place where democracy and freedom of speech are unquestioned values?

Then America would have been mighty indeed.

It is clear President Obama doesn't want to go to war in Syria. He regards it as too complex, too difficult, too uncertain.

American military action there would have a huge impact on the perception of America in the region - confirming every image he wants to change.

Yet the US is, perhaps, moving slowly and cautiously toward taking action. There is no sense of a time scale and no real certainty about what might be done.

This is very Obama: the caution, the desire to bring allies along, the reluctance to rush to judgment.

It is clear President Obama doesn't want to go to war in Syria. He regards it as too complex, too difficult, too uncertain.

American military action there would have a huge impact on the perception of America in the region - confirming every image he wants to change.

Yet the US is, perhaps, moving slowly and cautiously toward taking action. There is no sense of a time scale and no real certainty about what might be done.

This is very Obama: the caution, the desire to bring allies along, the reluctance to rush to judgment.

The Israelis say chemical weapons have been used. The UK says there is "limited but persuasive" evidence that sarin has been used.

Now the White House has sent a letter to two senators: "Our intelligence community does assess with varying degrees of confidence that the Syrian regime has used chemical weapons on a small scale in Syria."

That, Mr Obama has said for months, would be "a game changer". He has never exactly said, of course, how the game would change, but most people assume he meant military action of some sort.

White House officials have confirmed that if reports of past small scale use are confirmed, they would cross the president's red line. But he is not happy with the intelligence as it stands.

The letter goes on to say any such decisions depend on further "credible and corroborated facts that provide us with some degree of certainty".

It was perhaps an irony Mr Obama was speaking at the official opening of the George W Bush Presidential Library in Texas today.

It is easy to forget now that Mr Obama was elected almost as an anti-Bush - calm, deliberative, slow to wrath. He regarded the Iraq War as a serious mistake, the result of a mixture of bad intelligence and an enthusiasm for war.

The letter is pointed about this: "Given the stakes involved, and what we have learned from our own recent experience, intelligence assessments alone are not sufficient."

Already Republicans are saying the red lines have been crossed, that the Assad regime will feel emboldened if there is not action, that the investigation must not be outsourced to the United Nations.

It is clear Mr Obama doesn't want to go to war in Syria. He regards it as too complex, too difficult, too uncertain.

American action there would have a huge impact on the perception of America in the region - confirming every image he wants to change.

Yet the US is, perhaps, moving slowly and cautiously toward taking action. There is no sense of a time scale and no real certainty about what might be done. This is very Obama: the caution, the desire to bring allies along, the reluctance to rush to judgment.

Enemies call it dithering. Even allies are sometimes impatient. I doubt whether any of that worries a president who says sending young men and women into action is the hardest thing he has ever had to do.

A fake tweet, from the hacked account of a news agency, wiped $200bn (£131bn) off the New York Stock Exchange. It had claimed there had been two explosions at the White House, and President Obama had been injured.

It was quickly disclaimed and corrected, but some damage had been done.

The Wall Street Journal says much of the stock market reaction was down to automatic scanning of news sites, and instant adjustments. But I am not sure human traders would have been very much better than their machines at showing caution and not panicking.

It does show how central Twitter has become to our world.

Ever since news has been broadcast on the radio it has been possible to get information in real time - but you don't carry a radio with you everywhere, or check it all the time.

The addictive nature of Twitter makes it a powerful tool - and one without boundaries. Lies and truth appear without anyone trying to filter. Not that they should, but it puts a responsibility on the consumer.

Last week the Boston police did not tour the streets in a car and use a megaphone to tell residents of Watertown to stay indoors.

They tweeted it. They tweeted the end of the manhunt too, terse and triumphant. Amid this accurate information straight from the most important source, there was a lot of dross. The problem Twitter presents is how people filter it, and how much they trust it.

There is a danger Twitter itself becomes what is trusted, when it is only a publisher - you have to look to who is saying what. In one sense that is no different to going to a newsstand and choosing to buy one newspaper over another.

But it is different in scale - Twitter bombards, at least if you choose to subscribe to a wide range of people.

It is hugely valuable. My teenager daughter regards it as rather for losers - those who want to babble about what they had for breakfast.

When I first heard about it I thought much the same. Now it is probably the sixth thing I check in the morning. It is important for breaking news, fascinating for recommending articles and blogs I wouldn't have otherwise seen.

But lies and truth appear side by side. Not that there should be a filter, but it makes it all the more important people are more sophisticated, more discriminating.

As a journalist, I've long been irritated when people tell me: "They say…" "Who is the 'they' I ask? The BBC? The police? The government? The National Enquirer? The tabloid press?"

But for many it is an amorphous authority, the juiciness of the information more important than the veracity.

Twitter is indeed a powerful tool, and like all such instruments has to be treated with respect and caution.

It has been decided he will be tried in a normal criminal court, not by a military tribunal. He will not be treated as an "enemy combatant", which would mean he wouldn't be allowed the right to remain silent but would be interrogated to gain intelligence about the background to the attack.

The first decision is not particularly controversial, the second is. Several Republican politicians have already attacked the decision saying that it will limit the authorities' ability to gather vital intelligence.

President Obama made it clear shortly after he came to office that people would no longer be treated as unlawful enemy combatants - a term invented by the Bush administration as a new category for terrorists and al-Qaeda supporters fighting in Afghanistan who were not to be given the rights of either prisoners of war or criminals.

It has been decided he will be tried in a normal criminal court, not by a military tribunal. He will not be treated as an "enemy combatant", which would mean he wouldn't be allowed the right to remain silent but would be interrogated to gain intelligence about the background to the attack.

The first decision is not particularly controversial, the second is. Several Republican politicians have already attacked the decision saying that it will limit the authorities' ability to gather vital intelligence.

President Obama made it clear shortly after he came to office that people would no longer be treated as unlawful enemy combatants - a term invented by the Bush administration as a new category for terrorists and al-Qaeda supporters fighting in Afghanistan who were not to be given the rights of either prisoners of war or criminals.

It is a hugely sensitive tussle over the nature of Islamist terrorism, Islam itself and how America responds to terrorism and a religion it doesn't truly understand.

In many ways it is a replay, a reflection, and occasionally a distortion of the major disagreement between supporters of George W Bush and Barack Obama.

President Obama's opponents portray him as reluctant to use the word terrorism, overly sympathetic towards Islam, and insufficiently focused on the dangers of violent expressions of militant Islam. On the fringes, some accuse him of being a willing sympathiser.

But, more generally, there is a feeling on the right that liberals are too willing to bend over backwards to disconnect the religion from the violence.

This makes liberals hot under the collar. They see it as sheer bigotry, and point out that there is in fact no connection between millions of peaceful followers of a religion and a violent fringe.

It is not a debate restricted to politicians.

I, and I am sure other BBC colleagues, have received quite a lot of messages accusing us of, from one side, wilfully ignoring the role of radical Islam in this attack and, from the other side, saying we are fanning the flames of intolerance.

Some of the attacks on Obama are crudely party political.

He claimed that after the killing of Bin Laden and other major leaders al-Qaeda was "degraded" and by implication close to collapse.

His enemies say that is untrue, and he has failed. They want to argue that the strong hand of al-Qaeda is behind every attack.

As fundamental is the demand by leading Republicans that the suspect should be questioned as "an enemy combatant", even though he is an American citizen. The law allows this if a suspect is connected with al-Qaeda or similar organisations.

In part, that argument is one that goes back much further than Islamist militancy - to John Adams' defence of the British soldiers responsible for the Boston massacre, and all the way back to Magna Carta.

It is about whether hard-won rights for those accused of crimes can be abandoned when a government or a people feels under threat; if they are a civilised nicety, like good manners, that can be jettisoned in wartime, when the crime is too dreadful.

But it is also about how America looks at acts of terrorism. Many I spoke to in the last week regard attacks like the one at the Boston Marathon as a disgusting, horrific part of modern life.

One man queuing to go into the Red Sox game on Saturday specifically told me the British had got used to living with a threat because of the IRA. He felt America was moving into that phase.

Some think that is defeatist. For them America is at war. That forgotten phrase "war on terror" may come back into fashion.

They argue the country has grown forgetful and flabby since 9/11, and that the country should lead a global campaign against an existential threat.

President Obama will resist this. It is alien to his world view and distracts from his domestic agenda.

But if the rest of the year turns into the rehashing of a debate that had largely been buried, he will have lost.

People will want to know how far they delved, how hard they tried, how seriously they took the information. Some of the criticism will be unfair, based on hindsight - they must get thousands of such warnings ever year. Or perhaps they are quite rare. That is another question.

America has been in a kind of limbo while the identity of the bombers was unknown. With greater certainty the questions, and the politics, will begin.

People will want to know how far they delved, how hard they tried, how seriously they took the information. Some of the criticism will be unfair, based on hindsight - they must get thousands of such warnings ever year. Or perhaps they are quite rare. That is another question.

When the news broke that the second suspect had been caught Boston residents who'd been cooped up under a day-long curfew poured onto the streets whooping with joy.

A few minutes later twice that number of police cars, blue lights flashing. Then a phalanx of motorcycles. Most of them were police, but they looked like troops going to war. Later in the day Black Hawk helicopters circled overhead. All day inside the cordon, police having been going house to house, door to door, checking that people are safe, looking for the killer.

Around 20 armoured cars thundered into town. A few minutes later twice that number of police cars, blue lights flashing. Then a phalanx of motorcycles.