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Voters across America are preparing to take part in the biggest day of the 2020 election so far.

More than a year after the first Democratic candidates joined the race to take on Donald Trump, we've now reached Super Tuesday.

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.

By Wednesday, we could have a clearer picture of who the nominee will be.

What's happened so far?

Democrats across the US have been taking part in a series of caucuses (essentially party meetings, where you vote publicly at the end) or primaries (secret ballots) to pick their preferred candidate.

Bernie Sanders's success has come as a bit of a surprise. The Vermont senator lost out to Hillary Clinton in the 2016 race, but he isn't a typical Democrat by any means (in fact, he sits as an Independent in the Senate).

He's a staunch left-winger, so may struggle to convince the party's moderates if he becomes the candidate. He's also 78, and suffered a heart attack in the autumn. But he's proven extremely popular in the primaries so far across many age groups and ethnicities, and all the momentum is on his side.

The handful of moderate Democrats running have split the vote, so it's made it hard for any of them to break out (and this has helped Sanders build up a lead).

One of them, former vice-president and early favourite Joe Biden, underwhelmed before winning convincingly in South Carolina on Saturday. However, he has since seen a swell in momentum after centrist rivals Pete Buttigieg, and Amy Klobuchar quit the race to endorse him.

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Sanders does not have the left lane to himself either - Elizabeth Warren, the experienced Massachusetts senator, shares several of his policy objectives but has not lived up to expectations.

So might any of these candidates win the election in November? Honestly, it's too close to call, and there are so many unknown factors.

Why does Super Tuesday matter?

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.

Media playback is unsupported on your device Media caption Why Alexis and Amira could help decide the US election

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, will take part - the former for the first time on Super Tuesday.

Here's what is at stake in each state - the smallest to the largest - with some bonus nuggets of trivia thrown in.

Who will do best? A no-brainer: Bernie Sanders. He is one of the state's senators, after all.

Who could do well? Honestly? There's a chance no-one except Sanders will cross the 15% threshold of votes and get any delegates. He is extremely popular in his home state and won the 2016 primary here with 86% of the vote (though he eventually lost the nomination to Hillary Clinton). We could see the first results from here at about 19:00 local time (midnight GMT).

One piece of context In a poll by Vermont Public Radio in February, almost a third of people said the economy, jobs and cost of living were among the main issues on their minds - although Vermont has the joint-lowest unemployment rate in the country, at 2.3%.

State bird? Hermit thrush

Who will do best? We're going to start sounding repetitive, but polls point to Bernie Sanders. In 2016, he won more than double the number of delegates claimed by Hillary Clinton here.

Who could do well? There are more contenders than in 2016 which means Sanders' lead won't be as large. But billionaire Michael Bloomberg and Joe Biden are polling far behind.

One piece of context This isn't the only thing on the ballot on Super Tuesday in Maine. There's also a referendum on whether to reject a law that would block religious and philosophical objections to vaccinations.

State animal? Moose

Who will do best? Clue: his name is an anagram of Desire Banners. Sanders won here convincingly in 2016.

Who could do well? It's unlikely anyone will challenge Sanders. The most recent poll put Bloomberg in a distant second and former Indiana mayor Pete Buttigieg in third, before he dropped out. Could Bloomberg win votes that might have gone to Buttigieg, and tighten the gap on Sanders?

One piece of context Utah has not voted for a Democrat in the presidential election since 1964, when it picked Lyndon B Johnson. So whoever comes out on top here may not take the state in November.

State gem? Topaz

Who will do best? A recent poll by Hendrix College in Arkansas suggested Bloomberg's plan of concentrating on Super Tuesday states could pay off here.

Who could do well? Biden and Sanders possibly, although it's a close-run thing. Forecasting site FiveThirtyEight gives Biden a stronger chance - the vote could be split fairly evenly.

One piece of context It might not matter who Democrats pick: Arkansas has opted for a Democrat in a presidential election only twice in 40 years (and even then, it was local boy Bill Clinton, twice).

State dinosaur? Arkansaurus fridayi

Who will do best? It's tough to say. Biden, maybe just.

Who could do well? Bloomberg and Sanders, according to Oklahoma polling group Sooner last week.

One piece of context Fracking is a big issue here, and Sanders and Warren (who was born in Oklahoma City) have both proposed measures to ban it. The underground disposal of waste water used in fracking has led to a rise in earthquakes in this part of the US.

State beverage? Milk

Who will do best? We're in safe Biden territory. He has the support of plenty of senior Democrats in Alabama, and is widely liked among African Americans there.

Who could do well? Biden's lead in the polls looks fairly comfortable, but Bloomberg and Sanders appear most likely to challenge him.

One piece of context Republicans are also deciding who will run in November's Senate race, where they are very hopeful of ousting Democrat Doug Jones (and making it harder for Democrats to win the Senate later this year). The favourite right now is Jeff Sessions, Donald Trump's former attorney general.

State amphibian? Red Hills Salamander

Who will do best? It's close. FiveThirtyEight suggests Biden's chances here have improved a lot over the past few days.

Who could do well? There has been very little polling here, but it could well be Sanders, who was a distant second to Hillary Clinton here in 2016.

One piece of context In Tennessee, who votes may be a bigger issue than who wins - it has one of the worst voter turnout rates in the US. In the last presidential election, just over half of registered voters turned out, 10 points below the national average.

State wild animal? Raccoon

Who will do best? FiveThirtyEight gives Sanders a seven in eight chance of winning most votes here. You may notice that a picture is starting to form.

Who could do well? The site puts Biden in a distant second, with Elizabeth Warren just behind him.

One piece of context Once a Republican stronghold, out-of-state migration and population growth has turned Colorado increasingly "blue" - a Democratic tilt that extends down the ballot. In its latest predictions, election forecaster Sabato's Crystal Ball changed its rating of the state's US Senate race from "toss up" to "leans Democratic".

State cactus? Claret Cup Cactus

Who will do best? It was all set to be Minnesota senator Amy Klobuchar until she withdrew on Monday. She has now endorsed Biden, so... maybe Biden?

Who could do well? Sanders had been close behind Klobuchar in second, and is likely to pick up a decent amount of delegates here.

One piece of context This part of the US was badly hit by Donald Trump's trade war with China - advocacy group Tariffs Hurt The Heartland said businesses in Minnesota had to pay $797m (£604m) more in tariffs as a result. Will that translate into more support for Democrats in this election?

State mushroom? Morel

Who will do best? Sanders, maybe. But it will be close.

Who could do well? Elizabeth Warren, but it might be embarrassing if she doesn't win, given she is the senior senator for the state. Buttigieg's withdrawal may help her.

One piece of context A massive 40% of the candidates left in the race (two people) live in Massachusetts - as well as Warren, the other is Michael Bloomberg, who lives in Medford. Despite actor Michael Douglas campaigning for him there, he is not expected to do especially well here.

State fish? Cod

Who will do best? This will be a really interesting one to follow. The vote could be split fairly evenly between Sanders, Bloomberg and Biden.

Who could do well? See above.

One piece of context Watch the results in the Washington DC suburbs. This suburban vote will be crucial across the country in November's election (as it was in the 2018 mid-terms). How will the nationwide favourite, Bernie Sanders, perform there? Will moderates in the suburbs warm to him?

State dog? American foxhound

Who will do best? It's quite a similar picture to neighbouring Virginia, and will also be worth following - it's close between Sanders and Biden.

Who could do well? Bloomberg was polling well here at one point, but is drifting behind a little by now.

One piece of context This will also be a battleground state in November. As with Virginia, watch the crucially important suburbs of cities like Charlotte and Raleigh. But watch who they vote for, and whether that person ends up becoming the nominee. The way the votes go here in November might help decide the election.

State fruit? Scuppernong grape

Who will do best? We're into the big league now. It's very close between Sanders and Biden here. Either way, it looks likely Sanders will claim a large amount of delegates and by the time the results come in from Texas, his lead could be big.

Who could do well? It is likely to be a good night for Biden here too. Elizabeth Warren is third or fourth in most polls.

One piece of context There's reason to think that the so-called sleeping giant of the Texas Hispanic vote - now almost two million voters - is about to wake up. In the 2018 midterms, 46.9% of registered Hispanic voters turned out, a leap from 24.4% in 2014.

State crustacean? Texas Gulf Shrimp

Who will do best? If Sanders really does have an eight in nine chance of winning most votes here, as FiveThirtyEight predicts, you might as well call him the nominee. This is where Sanders' appeal to his "multiracial coalition" pays off - he looks like he could do well with African Americans, Latinos and Asian Americans here.

Who could do well? Right now, Biden looks like being a distant second.

One piece of context This will be a Super Tuesday debut for California. Lawmakers moved the state's primary up a month from its traditional spot in June in an effort to increase California's impact. The shift could matter: the country's most populous state will award 30% of the delegates on Super Tuesday.

State motto? Eureka!

*American Samoa (six delegates) and Democrats Abroad (13) are also voting on Super Tuesday