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In the run-up to Tuesday, Mr Biden and Mr Sanders both campaigned vigorously in Michigan, the biggest prize of the night with 125 delegates on offer. The stakes are particularly high for Mr Sanders, who is pinning his hopes of a resurgence on a win here.

The senator won a surprise victory in Michigan over Hillary Clinton in 2016, his message of protectionism finding favour in a traditional manufacturing state blighted by cuts to the car industry. Government mismanagement in Flint exposed children in the majority-black city to lead-poisoned waters, sparking furore and providing more populist enthusiasm for Mr Sanders’ message of fighting for racial equality.

In 2020, however, African-American voters have largely stuck with Mr Biden, who was vice-president to the first black US commander-in-chief; young voters have not turned out for Mr Sanders as he has hoped, and both Mr Biden and Mr Sanders are competing for blue-collar voters.

On Sunday, Mr Sanders’ campaign featured Jesse Jackson, the black pastor (who won Michigan during his 1988 primary campaign) and congresswoman Alexandria Ocasio-Cortez. Mr Biden’s featured Michigan Governor Gretchen Whitmer, who endorsed him.

Tonight, Sanders may face a make-or-break moment when the Michigan results come in.

This southern state could be a slam dunk for Biden.

Why?

The former vice-president has done very well so far with African Americans and Mississippi’s Democratic electorate is likely to be overwhelmingly comprised of black voters.

In 2016, the electorate was 41% African American and Sanders was beaten by Hillary Clinton by more than 65 points.

The BBC recently interviewed voters in South Carolina about the term "black vote".

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States across the country are voting. This means the results will be staggered across the next few hours.

Here’s when those polls close:

20:00 EST (00:00 GMT)

Mississippi

Missouri

Michigan - four of Michigan’s counties will close at 21:00 EST (02:00 GMT)

22:00 EST (02:00 GMT)

Idaho - some polls to close later, by 23:00 EST (03:00 GMT)

North Dakota

23:00 EST (03:00 GMT)

Washington state

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Washington state fell hard for Bernie in 2016, giving the Vermont senator a 45-point lead in delegates over Hillary Clinton.

This time, polls show Sanders clinging on to the slimmest of leads over Biden so we’ll have to wait till polls close to know for sure.

Tonight’s contest will make a change for the state. For the first time, Washington voters will choose their party’s nominee through a primary, instead of a caucus.

You may have had a chance to read how Vice-President Biden's voting record makes him vulnerable to attack from his rival Senator Sanders.

Read: Five areas where Biden is vulnerable

Well, some believe his temperament could be another area of weakness, and a confrontation he had with a voter today will add grist to the mill.

Some would say his colourful language shows him to be authentic - his critics would argue his verbal stumbles are a liability.

Watch the incident here - and make up your own mind.

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Let's profile a few of the states voting, starting with Missouri.

In 2016, Missouri had the distinction of being one of the closest contests. Bernie Sanders lost to Hillary Clinton by just about 1,500 votes.

The state’s electorate tends to be a bit older, with significant shares of black voters (around 21%) and white women (40%).

Both Sanders and Biden seem to think it could be a close race once again. Of the states voting today, Missouri has seen the second-most advertising dollars spent.

As of Thursday, Sanders had spent $524,000 and Biden had spent $484,000.

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A contest that once boasted two dozen candidates - white and non-white, men and women, youthful politicians and elder statesmen - has been winnowed down to a two-horse race after 20 primary contests.

The early running in the first three states was made by ex-mayor Pete Buttigieg and Bernie Sanders, with Joe Biden trailing further back in the pack.

But the first week of March brought a dramatic shift. With sweeping victories in 10 states on Super Tuesday, Biden has now collected the largest number of delegates - representatives who cast the ballots for the official party nomination - going into tonight’s primaries.

Congresswoman Tulsi Gabbard is the only other candidate remaining, but she has just two delegates.

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It’s looking good for Joe - if you believe the polls.

The former vice-president has a double digit lead over Senator Bernie Sanders, according to the latest national poll by CNN.

A solid 52% of Democratic-leaning registered voters say they want Biden, while 36% say they’d rather Sanders win.

And according to forecasting site FiveThirtyEight, Sanders’ chances of a comeback are slim.

Biden’s surge on Super Tuesday (note the pink line spike on the chart) has made him the 95% sure favourite to win the Democratic nomination.

But this race has been full of surprises so...

Well, as the coronavirus infections pick up pace around the country, caution is the word of the day. Some countries have banned large gatherings, others have cancelled events altogether.

Here in the US, this is not policy yet, but both Bernie Sanders and Joe Biden have called off tonight's schedulled rallies in Cleveland, Ohio.

Senator Sanders expressed "his regret to the thousands of Ohioans who had planned to attend" - and former Vice-President Biden thanked those who had planned to be at the rally, hinting this could be the case with future rallies, too.

"We will continue to consult with public health officials and public health guidance and make announcements about future events in the coming days," he said.

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A primary is an election held across a state to pick a party's nominee to run for office (in this case, the presidency). Voters pick their candidate in a secret ballot.

There are a few types. An "open" primary is open to all registered voters in that state, and they can vote for any candidate. A Republican voter can vote in the state's Democratic primary, and vice-versa.

In a "closed" primary, only registered voters affiliated with each party in that state can vote.

The more votes a candidate gets in a primary, the more "delegates" they are awarded, and all candidates will be hoping to win an unbeatable majority of delegates.

Image source, Getty Images

Welcome to our live coverage of ‘Mini Tuesday’, where we will share results and analysis from the latest states to cast primary votes on this 10 March, 2020.

The contest has effectively come down to a race between two septuagenarians pitching two disparate paths for the party this election year.

Bernie Sanders, an unabashed left-winger promising a political “revolution” held the early lead. But his front-runner status was shattered after centrist Joe Biden mounted a stunning political comeback on Super Tuesday.

Will the momentum behind Biden, 77, continue to push him past Sanders, 78, in votes tonight? Six states - Idaho, Michigan, Missouri, Mississippi, Washington and North Dakota - will have their say.