Chris Wallace asks Biden about the protests that swept the US this summer, narrowing in on the 100 days of protests in Portland, Oregon - some of which turned violent.

"As the Democratic nominee, have you ever called the Democratic mayor of Portland or the Democratic governor of Oregon and said 'hey, you've gotta stop this?'"

Biden's response is simple: "I don't hold public office now."

But, he says, "violence should be prosecuted".

It's an important topic for the former vice-president: his opponent is telling voters that he alone is the candidate of choice for those who seek law and order across the country.

Image source, Reuters

Image source, Getty Images

Can't handle the interruptions between candidates? Neither can the moderator.

After about an hour of debate - featuring bickering, cross-talk and insults between candidates - Chris Wallace pleaded with Trump and Biden to rein it in, breaking into a brief shout in the process.

"Gentleman! I hate to raise my voice, but why should I be different than the two of you?"

The country will be better served with fewer interruptions, he says. Cut off by Trump, Wallace tells the president that he's a bigger offender than Biden.

Ritu Prasad
BBC News writer, Fort Myers, Florida

We've been asking our readers for their most pressing questions about the US election. now it's our turn to respond.

Click here if you want to know more, or to send us a question of your own.

Bill K, 17, from Newport, Rhode Island asks: What are Trump’s and Biden’s attitudes towards the Black Lives Matter movement?

Trump and Biden are both fielding questions on race and the unrest in a number of US cities tonight.

Here’s a look at what they’ve said about Black Lives Matter (BLM) in the past.

If Make America Great Again was Trump’s 2016 mantra, “law and order” may be his 2020 motto. Trump has been a staunch defender of police authority throughout the summer’s protests - and BLM has certainly drawn his ire.

At a campaign event for black voters last week, he called BLM an “extreme socialist” group that was “destroying many black lives”. He’s labelled BLM as “Marxist” and “discriminatory”, and said the slogan is a “symbol of hate”.

In contrast, Biden's Democratic National Convention went all out with its message against racial injustice. Family members of George Floyd and Eric Garner - two black men who died in police custody - spoke during the first night. Hillary Clinton and Barack Obama both referenced BLM in their speeches. Biden called for an end to the “stain of racism”.

Some of the policies called for by protesters have made it into the Biden platform. These include national policing standards, addressing systemic misconduct, investing in black communities, and other criminal justice reforms.

He does not, however, call for defunding the police. More on that here.

Reality Check

Biden has criticised Trump’s management of the coronavirus response. “We in fact have 4% of the world’s population, 20% of the deaths,” the former vice-president said.

That’s about right - according to the figures. The US population is about 328 million, which is just over 4% of the estimated population of the world of around 7.7 billion.

There have been 205,942 deaths recorded in the US, according to the latest John Hopkins University data. The total number of deaths recorded worldwide is 1,004,808.

That means the US does account for about 20% of global Covid-19 deaths, although the way countries record mortalities varies considerably.

Here's more fact-checking of Trump's coronavirus claims.

Anthony Zurcher
BBC North America reporter

When the New York Times story about Trump’s taxes broke on Sunday night, it was viewed as a bombshell – the public was finally getting a look at information the president had, in a break with tradition, withheld for years.

When the topic came up in the debate, Trump offered a similar defence to the one he provided in 2016 – that he had paid plenty of taxes and his ability to avoid a larger tax bill was simply his taking advantage of the law.

Biden, for his part, tried to turn the topic into a condemnation of Republican-backed tax changes. While he noted that Trump paid less in federal taxes than school teachers, that message – which could have been a powerful attack – got buried in ensuing scuffle with the president.

If Trump’s tax returns have any legs as an issue in this campaign, it won’t be because of this debate.

Image source, EPA

Moderator Chris Wallace points out that the first three years of the Obama-Biden White House saw more US jobs created than the first three years of the Trump administration.

"It was the slowest recovery since 1929," Trump retorts.

Biden points out that the US economy was badly suffering when he became vice-president in 2009, a result of the so-called Great Recession.

Biden hits out at Trump: "We handed him a booming economy. He blew it."

Trump goes on to claim the US economy will tank if Biden wins.

There has been an interesting contrast in styles between the two candidates throughout the debate.

While the former vice-president has made a point of addressing the camera directly and making appeals to the unseen television audience, the president has trained his eye on Biden throughout the debate.

Trump has not shrunken from personal barbs, and halfway through the evening launched his first attack against Biden's son, Hunter, whom he has accused of having nefarious ties to Ukraine.

Biden replies, looking at the camera: "This is not about my family or his family. It's about your family,".

"It's about you, the American people. That’s what we’re talking about here."

We've just been listening to the candidates battling over the economy. And once again, taxes are a subject of dispute.

Wallace flat out asks Trump: "Is it true that you paid $750 a year in federal income tax each of those years? [2017 and 2016]"

"I paid millions of dollars," Trump says. "I paid $38m one year. I paid $27m one year."

Biden challenges him to reveal his taxes and Trump says "you'll see it when it's finished" - referring to an audit his taxes are under. But, there's no legal reason why he can't reveal them now.

Image source, Reuters

Wallace tries to get back to the question. "Will you tell us how much you paid in federal income taxes in 2016 and 2017?"

"Millions of dollars," Trump says. "And you'll get to see it."

Trump says it was the tax laws that gave him tax credits, and accuses Biden of passing the tax bill that gave developers like him all these benefits.

Biden replies that it's Trump's tax cuts that benefit the rich and that he's going to eliminate them and invest in those who need help instead.

We've spelled out everything to know about the Trump tax controversy here.

Anthony Zurcher
BBC North America reporter

The coronavirus was always going to be difficult terrain for the president. He had to defend a response that has resulted in more than 200,000 American deaths. He did so by saying the steps he’s taken prevented more deaths from taking place, and suggesting Biden would have made things worse.

Biden’s reply was to talk directly at the camera, asking the viewers if they could believe Trump (polls indicate a majority of Americans disapprove of Trump’s handling of the pandemic).

In one telling exchange, Trump boasted about the size of his campaign rallies – held outside because that’s what the “experts” – with emphasis on that word – suggest. He then said Biden held smaller rallies because he couldn’t attract larger crowds.

It represents a fundamental difference in the way the two candidates view the pandemic and whether the situation is getting better – or worse.

Image source, Reuters

Reality Check

Trump has claimed that, prior to the coronavirus outbreak, “we built the greatest economy in US history”.

He claims to have generated historic economic growth, record low unemployment, and lifted millions of Americans out of poverty.

It's true the economy was doing well before the pandemic - continuing a trend that began during the Obama administration - but there have been periods when it was much stronger.

You can read more about the economy under President Trump here.

Reality Check

A little earlier the candidates clashed over how many people in the US have pre-existing medical conditions.

Pre-existing conditions can stop some Americans from being covered by private medical insurers in the US.

Biden said there were 100 million people with pre-existing conditions, but Trump said that number was “totally wrong”.

So how many are there? There is no definite answer.

According to the US government’s Department of Health and Human Services, 50 to 129 million non-elderly Americans have some type of pre-existing health condition.

Other organisations have different estimates. The Center for American Progress put it higher, at 135 million people under age 65, and another non-profit foundation has put it lower at 54 million.

Moderator Chris Wallace asks the candidates about the US economy and their plans for recovery after coronavirus lockdowns.

"The economy is recovering faster than expected since the shutdown," Wallace says - throwing a bone to Trump. "The hit to growth is not going to be nearly as big as forecasters expected."

Taking the first shot, Trump defends his promise for a V-shaped recovery by returning to a favourite refrain: "I built the greatest economy in history".

We’re just over a third of the way into the debate, and here’s what some members of our voter panel are thinking.

Brian, undecided voter: “I think Biden is doing a pretty good job of ignoring Trump’s interruptions. We knew Trump was going to interrupt people. Biden had to have some way to address it, and he’s doing that well.”

Ariel, Trump voter: ”I don’t think Trump has been as aggressive as he could be and Biden is much more aggressive than I expected.”

Keirsten, undecided voter: “It doesn’t even seem like they’re at the same place. There’s no control over letting one finish their thoughts."

Josh, Biden voter: "I was expecting [Biden] to gaffe a little more. He's talking effectively and coherently and so far he's doing a good job. And his arguments are straightforward."

Meet the voters we’re watching the debate with tonight.

Image source, EPA

A little colour from the scene: A journalist in the debate hall reports that several of the Trump family entered without masks, despite rules that obliged everyone in the room to wear them.

A Cleveland Clinic doctor in a white lab coat then began approaching the Trump family's guests, offering them masks in case they hadn't been offer one. Nobody she prompted responded by wearing one.

The doctor declined to comment to press, and a debate hall staffer was overheard telling her: "That's all you can do".

Joe Biden's granddaughter Naomi made her disapproval plain on Twitter...

Biden accuses Trump of covering up the seriousness of the virus (you may recall all the headlines about the Bob Woodward book earlier this summer, click here for a refresher) and says: "A lot of people died and a lot more are gonna die unless he gets a lot smarter, a lot quicker."

Now we get into a churlish exchange over "smarts".

"Did you use the word smart?" Trump asks. "You said you went to Delaware State [university] but you forgot the name of your college." Biden laughs and says he didn't say that, but Trump continues.

"You graduated either the lowest or almost the lowest in your class. Don't ever use the word smart with me. Don't ever use that word."

Biden interjects: "Oh, give me a break."

"Because there's nothing smart about you Joe," Trump goes on. "Forty-seven years you've done nothing," he says, referring to the number of years the former vice-president has served in elected office.

"Well let's have this debate and we'll see," Biden says.

Support for Donald Trump’s handling of the coronavirus pandemic fell to its lowest point among Republicans in July, according to data from Ipsos, a leading polling company - but it has recovered a little since then.

The last time a majority of Americans approved of his handling was back in April, the data suggests.

Biden continues to criticise Trump's handling of the pandemic. "This is the same man that told you by Easter it would be gone," Biden says of the president.

He refers to Trump's musing that some sort of solvent, like bleach, could be injected to cure people of the virus.

“Maybe you could just inject some bleach in your arm and that would take care of it,” says Biden.

"That was said sarcastically and you know it," says Trump.

The debate is still getting going, but the candidates are already getting scrappy: bickering and cutting each other off.

Amid the squabbling, we've already heard Biden asking Trump to just "shut up", and some viewers are asking if moderator Chris Wallace could make both of the candidates do just that by muting their microphones while their opponent takes a question.

Anthony Zurcher
BBC North America reporter

Image source, Getty Images

So this is the kind of debate it’s going to be.

It was predicted that Donald Trump’s objective during this debate was to rattle Joe Biden – and within minutes it became clear he planned to do this by constantly interrupting the former vice-president.

That’s made for a series of chaotic exchanges, that included Biden calling Trump a clown and asking, indignantly, “will you shut up, man?"

As moderator Chris Wallace announced that the coronavirus was the next topic and that both candidates would have two and a half uninterrupted minutes to answer, Biden quipped: “Good luck with that”.

Uh, yeah. Moderating this free-for-all may be the worst job in America right now.