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How did just a regular Tuesday become so super?

It hasn’t always been like this. Back in 1976, only six primaries or caucuses were held on one Tuesday (and that was in May). But over time, as states battled to be closer to the start of the primary calendar, and play a more important role in deciding the nominees, that has changed.

In 1988, Democratic leaders from southern states bandied together to hold their votes on the same day, in the hope that this would help a southern candidate lead the contest. It didn’t work out - Al Gore and Jesse Jackson split the southern vote, and Massachusetts Governor Michael Dukakis squeezed through to become the nominee. (The plan worked the next time round with Bill Clinton).

Super Tuesday has been even more super than this year - in 2008, 24 states voted on the same Tuesday, and half of all delegates were on the table in just one day. Today’s 14 states and one-third of delegates make this, relatively, a nice low-key affair.

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Does your candidate have one (or several) celebrity backers? You may be surprised to learn that it is not a superfluous question. Famous endorsements can be worth alot. In 2008, for example, economists found that Oprah Winfrey's support for Barack Obama could have earned him as many as one million additional votes in the primary election, external.

This time around, there are endorsements aplenty from Hollywood. But it might not always be obvious who is the favourite option of Cardi B, Tom Hanks and Gwyneth Paltrow. Why not try our quiz and see?

Anthony Zurcher
BBC North America reporter

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A flurry of new post-South Carolina polls suggest that Joe Biden has recovered from his month-long campaign swoon and is once again challenging Bernie Sanders for the lead both nationally and in key primary states.

A Morning Consult survey released on Tuesday, external, for instance, saw a 10-point swing for Biden over its poll just a few days before, putting him up 36% to 28% over Bernie Sanders.

The problem for the former vice-president, however, is that voters have been casting their ballots for weeks now in many of the most important Super Tuesday states.

California – the biggest prize, with 415 national convention delegates at stake – started its early voting process on 3 February, the day of the Iowa Caucuses. Estimates are that more than 40% of the total primary vote has already been cast – much of it when Biden was mired low in the polls and written off by many.

Texas, another key state, has had more than a million early votes cast, many at a point when it looked like former New York Mayor Michael Bloomberg was the most viable moderate candidate on the ballot, not Biden. Given that only 1.4 million Texas Democrats voted in the 2016 presidential primary, the Texas results could end up reflecting the politics of a week ago, not today.

The trend-lines are still looking good for Biden, and there are plenty of delegate-rich states to vote in the weeks ahead, but if he comes up short he may be left wondering what would have happened if more people had waited a bit longer before casting their Super Tuesday ballots.

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It's all about the delegates.

Let's say Candidate A gets the most support in one state. Candidate B does OK, but not as well. Candidate A is then awarded the most delegates, and Candidate B fewer. The number of delegates available differs in each state.

Later in the summer, those delegates will then vote for their candidate to become the Democratic nominee. The target for any candidate is to reach an unbeatable majority of 1,990 delegates.

This is where Super Tuesday comes in.

Up to now, only 155 delegates have been awarded in four states. On Super Tuesday, a massive 1,357 delegates will be distributed, and 14 states are voting. The two most populous, California and Texas, are taking part - the former for the first time on Super Tuesday.

Want to know more? Here's your primer on the biggest day in the 2020 election so far.

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Welcome to our live coverage of Super Tuesday: the biggest day yet of the 2020 election.

More than a year after the first Democratic candidates joined the race to take on Donald Trump, we've now reached the campaign’s most critical point so far.

Fourteen states will vote on which Democrat they want to run in November's election. Bernie Sanders is in the lead after the early contests.

In just a few hours, we may have a much clearer picture of who the nominee will be.