Image source, Getty Images

We're winding down our coverage of the Democratic presidential primaries.

Joe Biden claimed victory in Michigan, Mississippi and Missouri - vaulting the former vice-president further ahead of rival Bernie Sanders.

It's not yet clear who will win the remaining states - North Dakota, Washington and Idaho.

What is clear is that Joe Biden now has tightened his grip on victory.

Now that polls have closed. we're looking to see which of the two leading candidates - Joe Biden and Bernie Sanders - have won each of the six states that voted today.

But the number that really matters is the delegate count.

The primaries and caucuses are all about winning delegates - party members from a state who pledge to endorse a candidate at the party conventions in July. The number of delegates varies from state to state.

The target for any candidate is to reach an unbeatable majority of 1,990 delegates.

As of now - and this will change as results trickle in - Joe Biden boasts 813 delegates, a sturdy lead over Bernie Sander's 656.

Image source, Getty Images

Need a little background? Looking for some context?

Here are some great explainers:

BIG PICTURE: All you need to know about presidential race

SIMPLE GUIDE: What are the primaries and caucuses?

ISSUES: See how Biden and Sanders compare to Clinton, Obama and LBJ

TURNOUT: Why don't more young people vote?

BIDEN: Five areas where he's vulnerable

SANDERS: Do his spending plans add up?

The US is facing an outbreak of coronavirus across the country, and two states voting today have been affected.

One confirmed case has been reported in Missouri and Washington has the highest number of reported cases - 270 - of any US state.

But the show (election) must go on.

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

As that AOC speech shows, no-one in the Democratic race has been able to harness youth support like Sanders.

The BBC's Anthony Zurcher writes:

Once again, he performed best with ages 17 to 29, according to exit polls. He carried it 82-15 in Michigan and 76-19 in Missouri, and only lost it by 4% in Mississippi, despite being routed in the state.

The problem for the Vermont senator, however, was that the age group averaged only 12.5% of the electorate in those three states - not nearly enough to save the day for Sanders. The epitaph for his campaign may be that it was premised, in part, on the passion of new young voters who simply did not show up in sufficient numbers at the polling booths.

While this may be good news in the short term for Biden, it is a flashing warning sign for the general election if he is the nominee. Young voters were a key part of the coalition that delivered the White House to Barack Obama in 2008, as he won them by a record 34% over John McCain.

If the former vice-president does not find some way to improve his standing with this age demographic, he may suffer the same fate as Hillary Clinton, who only won the youth vote by 18%.

Read more: Why don't more young people vote?

Image source, Getty Images

New York Congresswoman Alexandria Ocasio-Cortez - progressive darling and Bernie Sanders' star surrogate - took to Instagram Live this evening as tonight's results looked increasingly dim for her candidate.

"There's no sugar coating it," she said to the nearly 10,000 users watching. "Tonight's a tough night for the movement overall."

Describing a "stark" generational divide" - younger voters for Sanders, older voters for Biden - Ocasio-Cortez told followers it was time to "leverage" support for Sanders and his policies, like Medicare for All.

“Now is the time to ask for accountability. And now is the time to ask for commitments - real commitments - not just gestures.”

The final polls of the night - Idaho and Washington - have closed.

Votes are still being counted in North Dakota.

It is still too early to call the results for any of these three contests.

Anthony Zurcher
BBC North America reporter

On a cool Tuesday evening at the University of South Florida campus in Tampa, Florida, Bernie Sanders supporters gathered to plan and give themselves a pep talk for the final week before the state’s primary.

A young campaign worker told the crowd of students that the establishment - Democratic rivals, the media and big corporations - were organising against their candidate. But while they couldn’t control what happened on Super Tuesday last week or in Michigan, Washington and other states tonight, they are the ones that get to decide whether Sanders wins in Florida and in their town and their precincts.

After another rought night tonight, his back will be to the wall, and he’ll need a good result in Florida, as well as other big states holding primaries next week, such as Illinois and Ohio.

Maria Zamora and Sharman Hashmi, who attended the event, say they are still optimistic about Sanders’ chances.

“Sanders really stands behind the people who haven’t had a voice for a long time,” Zamora, who is on staff at the university, says. "I feel like those people are going to support him no matter what."

In the midst of another promising night - compounding his already commanding lead - Joe Biden thanked supporters and celebrated his political comeback.

Just a week ago, pundits declared this campaign dead, he said.

"Now we're very much alive.

"It's a comeback for the soul of this nation.

"I take nothing for granted, I want to earn every single vote in every single state."

Earlier we brought you their healthcare and education differences.

The third and final policy to explore is the one many believe to be the most important of all - climate change.

They both believe cimate change is real, and that President Trump's decision to withdraw from the international Paris climate agreement was wrong.

But their solutions differ.

Mr Sanders has been touting his "Green New Deal" - a $16.3tn (£12.5tn) package that he says would create 20 million jobs and pay for itself over 15 years.

Mr Biden's plan envisages eliminating net greenhouse gas emissions by 2050 - with targets going beyond Mr Obama's goals. His plan would cost $1.7tn for the first decade, alone.

Anthony Zurcher
BBC North America reporter

Image source, Getty Images

Mississippi was the first state to be called for Biden on Tuesday, and it was only the latest example of the strengths of his campaign - and another reason why the former vice-president appears to be in the driver’s seat as the primary season unfolds.

As in South Carolina - the state that started Biden’s political revival - more than 60% of the Mississippi electorate is black. And, as in South Carolina, the former vice-president dominated that demographic, to the tune of 86-11. The common refrain that a Democrat can’t win the nomination without the support of black voters, somewhat in doubt after Sanders’ dominating win in the Nevada caucuses, now seems to once again be an ironclad rule.

The Mississippi result is also important because of what it means for the delegate calculations that will determine the nomination. Biden isn’t just winning the state, he’s dominating it. He’s going to win the lion’s share of the state’s 36 delegates to the national convention, further extending his delegate lead. Given that delegates are awarded proportionally, to catch up Sanders would have to start winning in some states by similarly large margins.

Barring some sort of drastic change in the race, that seems unlikely in the extreme. With every state Sanders loses, he falls farther behind - and the more improbable his comeback would be.

Bernie Sanders will not address his supporters tonight, says CBS.

The news comes during a disappointing night so far for the Vermont senator - he has lost to Joe Biden in all three states to report results.

Results from three potentially more favourable states - North Dakota, Idaho and Washington - are to come.

A lot.

Senator Sanders is promising a revolution in the US.

His supporters see his policy goals as the kind of overhaul the country needs to fix deep-seated problems.

But his critics have accused him of trying to turn the country of free enterprise into a socialist state-run republic that entrusts the government with a lot more than Americans are used to.

For instance, nationalised universal health care, cancelling student debt, and plans to tackle climate change would cost an additional $40tn in government spending over the next decade alone.

Sanders says he will raise money through new taxes and the savings earned from his reforms are massive.

Critics say his costing figures do not add up. Do they? The BBC's Reality Check did the maths.

Read here what they found out.

Image source, Getty Images

Polls in Idaho close in 40 minutes.

Generally a Republican-safe state in presidential elections, it was the nation’s fastest-growing state last year, bringing its population to nearly 1.8 million.

With such a surge, some wonder if the added voters could turn this red state (meaning Republican-leaning) a little more blue (favouring Democrats).

Idaho Democrats will also be participating in a primary for the first time - they’ve used caucuses in the past - which may have an impact on voter turnout, and the results overall.

Either way, results today could give us a hint of what is to come in November’s general election.

Image source, Getty Images

Bernie Sanders is projected to lose Michigan, a state where he drew an adoring crowd of about 10,000 just two days ago.

Jonathan Turley, a law professor and BBC contributor who was visiting the college campus in Ann Arbor, spoke to supporters. He found clues that explain both the senator's popularity with young people - and also the limits of his appeal with his own older generation.

Now, he has not just the numbers but the movement that he always dreamt of. Indeed, he is the movement. While some might not want socialism, everyone in this crowd desperately wants Sanders.

Arden Shapiro and Hazel Gordon are precisely why the Democratic establishment is so worried about this movement - and so seemingly incapable of tapping into its energy. While they would vote for Biden if forced to in an election against Trump, they see Sanders as the only true and clear voice in the race.

Arden said that she was "really angry" about the level of corporate control in our system perpetrated by both parties. A trans woman, Hazel said that she saw Sanders as the only person truly fighting to help people secure medical insurance, particularly mental health coverage.

Hazel said that she viewed Biden as taking the side of corporations and did not support anything she believed in. Arden would later help introduce Sanders at the rally and called on her fellow students to bring five friends to the polling places to secure a win in Michigan over the establishment.

Others were even more direct. There were the guys distributing "Eat the Rich" T-shirts. Another supporter carried a sign reading "Make Racists Afraid Again". Those images unnerve many traditional Democratic voters who see this movement as potentially careening out of control.

Read Jonathan's full viewpoint piece.

Image source, Getty Images

Let's take a step back from the horse race tonight and take a wider view on the election.

Here are some great explainers:

BIG PICTURE: All you need to know about presidential race

SIMPLE GUIDE: What are the primaries and caucuses?

ISSUES: See how Biden and Sanders compare to Clinton, Obama and LBJ

TURNOUT: Why don't more young people vote?

BIDEN: Five areas where he's vulnerable

SANDERS: Do his spending plans add up?

Anthony Zurcher
BBC North America reporter

Image source, Getty Images

Four years ago, Michigan gave Bernie Sanders a surprise win - albeit a narrow, 49-48 one - breathing new life into a campaign that was struggling after Hillary Clinton dominated Super Tuesday.

This time around, the mid-western state could mark the beginning of the end for his campaign.

The difference, according to exit polls, were white voters, union voters and college graduates. Sanders won all three groups in 2016. On Tuesday night, Biden put them in his column. He carried college graduates 51-44, whites 51-45 and union members - 30% of the primary electorate - 54-42.

Add that to Biden’s already strong performance among black voters, late-deciders and those who are looking for someone who can beat Donald Trump, and it’s the recipe for a comfortable win for the vice-president.

The ease of the result will raise new questions about whether the 2016 Michigan primary was a reflection more of Clinton’s weakness rather than Sanders’ strength. At the very least, it’s evidence that rather than improving on his 2016 performance, the Vermont senator is falling short.

And if he’s falling short in Michigan, his window to the Democratic nomination is on the verge of slamming shut.

Image source, Getty Images

Former Democratic candidate and self-declared "Asian math guy" Andrew Yang has endorsed Joe Biden for the nomination.

This race is about "getting real solutions in place," Yang said, adding that Biden called him last week.

"We had a really great conversation."

"I wanted to let the Democratic process play out and I believe it has," Yang said, explaining why he had not endorsed earlier.

"We need to come together as a party, starting tonight."

Want to know more about the Yang Gang?

Read about the political novice and his devoted base here.

Image source, Getty Images

For voters in Washington - the centre of the US coronavirus outbreak - the vote may be overshadowed by the ongoing spread of Covid-19.

So will it hurt turnout?

There's good reason to think it won't: Washington is one of a handful of states that conducts elections entirely by mail.

All registered voters get a ballot sent to their address about two weeks before election day and they have two weeks to send it back in - meaning there are no polling places, door handles, or necessary physical contact.

Still, Covid-19 hasn't been forgotten - officials have urged voters not to seal their envelopes with a lick.

Because of all the postal votes to count, we might not get a result called from Washington state tonight.

Image source, Getty Images

As results come in across six US states, Donald Trump's campaign released a statement calling Joe Biden and Bernie Sanders "two sides of the same coin".

"The Democrat candidate for president will be running on a big government socialist agenda regardless of the name on the ballot."

"Either way, President Trump is on an unstoppable drive toward re-election.”

As expected, Trump has won the Republican contests in Mississippi, Missouri and Michigan. Technically, he is not the official Republican candidate until it is announced at the convention.