Super Tuesday is the biggest day of the Democratic primary campaign. Fourteen states will hold nominating contests to pick who they think should square off this fall against likely GOP nominee President Trump.

There are 1,357 delegates at stake, about a third of all delegates. So far, fewer than 4% of the delegates have been allocated.

People will head to the polls all across the country, from Virginia to California, Tennessee to Texas. The states and voters are diverse. Almost half have significant black populations, and Latinos figure to be an important factor in the two states with the biggest delegate hauls, California and Texas.

There's a lot on the line, especially for Sen. Bernie Sanders of Vermont and former Vice President Joe Biden. Sanders is the front-runner . He's built a strong organization in these states that's been buoyed by a multimillion-dollar ad campaign. Biden is lagging, but hopes to ride a wave of momentum from his big win in South Carolina Saturday.

And then there's Mike Bloomberg. After spending hundreds of millions of dollars, Bloomberg will be on the ballot for the first time. Does he surprise and emerge as an alternative to Sanders, or will he siphon votes from Biden? And what impact might remaining candidates , including Sens. Elizabeth Warren and Amy Klobuchar, have?

Here's what to watch for and what you should know about each of the Super Tuesday states, in order of most pledged delegates. (Note: American Samoa and Democrats living overseas are also voting on Tuesday.)

California

Delegates at stake: 415
Polls close: 11 p.m. ET

This is the most important state of Super Tuesday because of its size. Its 415 delegates is more than the nine Super Tuesday contests with the lowest delegate totals combined.

Latinos are expected to make up about 30% of the electorate . Sanders won Latinos overwhelmingly in Nevada , and if he runs up the score with them in California, he could be build a formidable pledged-delegate lead.

Sanders is the heavy favorite here, despite losing to Hillary Clinton in 2016 . He's spent about $7 million on ads (of the $15.5 million he's spent across Super Tuesday states), according to data as of Feb. 27 from Advertising Analytics provided to NPR.

Biden has spent $0 on California TV ads, and just $4,000 (yes, that's thousand) on digital. A ray of hope for Biden is also that even though early voting started a month ago, fewer ballots have been returned than in past elections.

Bloomberg, in contrast, has spent more than $71 million and is currently polling below the 15% threshold required to get any delegates in all of these contests.

Warren is teetering around the delegate threshold percentage, too, with most polls conducted before South Carolina. Does she get above 15%? Does she pull from Sanders? Does Biden gain momentum from South Carolina?

A wild card is black voters. There were no exit polls in 2016; 2008 exit polls showed black voters were only 7% of the electorate . But the California Democratic Party estimates that African Americans are about 16% of the party. Do they turn out? Depending on which estimate winds up being correct could determine if Biden makes a dent in the state.

This will also be the first significant measure of Asian Americans in this election. They were 8% of the electorate in 2008, and the California Democratic Party estimates they are 10% now.

Texas

Delegates at stake: 228
Polls close: 9 p.m. ET (Most polls close at 8 p.m. ET, but El Paso is in the Mountain time zone.)

Everything's bigger in Texas, including the delegate count. OK, it's not as big as California, but it's right up there.

The race is shaping up to be closer than in California. Polling shows Sanders up by an average of 9 points over Biden. Bloomberg is the only other candidate averaging above the 15% threshold needed to get delegates, but whether he makes it is something to watch. Some polls have also shown Warren at or above the threshold, too.

This state has not always been friendly to Sanders. He lost it to Clinton by more than 30 points in 2016. A number to watch on Tuesday is 33%, the percentage of the vote he got the last time around.

Sanders struggled because Clinton had a fairly strong hold on voters of color, and Texas is expected to be a majority-minority electorate Tuesday. In 2016, it was 57% non-white , including 32% Latino and 19% black.

Also key to watch is the age of the electorate that comes out. Sanders has had his biggest advantages with younger voters — and Biden with older voters. The numbers to watch: 20%, the percentage of the electorate in 2016 that was under 30; and 18%, the percentage over 65.

Biden's disadvantages here are advertising and early voting. He's only spent about $89,000 here compared to more than $3.7 million for Sanders. Early voting lasted for 10 days , until Friday, the day before Biden's boost in South Carolina. More than 1 million Democrats voted early.

North Carolina

Delegates at stake: 110
Polls close: 7:30 p.m. ET

Black voters are key. About a third of the electorate in 2016 was African American.

Sixty-one percent were also 45 and older.

Both groups favor Biden, but the percentages of both are lower in North Carolina than in South Carolina .

That means a narrower race between Biden and Sanders. Polls show Biden slightly ahead of Sanders , and the only other candidate polling at or near threshold is Bloomberg, who has spent almost $15 million on ads in the state. Warren hasn't been over 15% in the state in almost two months.

Virginia

Delegates at stake: 99
Polls close: 7 p.m. ET

Virginia, with its 7 p.m. ET poll-closing time, will give an early indication of whether moderate Democrats are coalescing around Biden. This is a place Clinton won by almost 30 points over Sanders, and Biden has now gotten the endorsements of former Gov. Terry MacAuliffe and Sen. Tim Kaine, also a former governor.

Unite the Country, a superPAC supporting Biden, believes Biden is starting to do well not just with black voters but with white women over 40. The Virginia suburbs is the place to prove it.

Clinton won almost two-thirds of white women , who were 36% of the electorate, in addition to blowing out the margins with black voters. She won 84% of African Americans, and they were about a quarter of the electorate.

There haven't been many good polls in Virginia. The last best one was a Monmouth poll from Feb. 18 , which is a lifetime in a presidential primary race. It showed essentially a three-way tie between Sanders (22%), Bloomberg (22%), Biden (18%) — and it was conducted before Bloomberg's first debate in Las Vegas, which was a spotty performance.

Massachusetts

Delegates at stake: 91
Polls close: 8 p.m. ET

This is Warren's home state, but Sanders is making a play here in this state where 85% of Democratic voters in 2016 were white . Sanders is actually leading very narrowly in most polls . But with no one else polling above threshold — and with former South Bend, Ind., Mayor Pete Buttigieg out of the race — Sanders and Warren may split the delegates evenly here.

Minnesota

Delegates at stake: 75
Polls close: 9 p.m. ET

Another home-state advantage here, this time for Minnesota Sen. Amy Klobuchar. Klobuchar has struggled after her surprise third-place finish in New Hampshire , but she has fizzled since. Minnesota could be her last stand Tuesday night.

There hasn't been a lot of polling, but what does exist shows Klobuchar doesn't have an overwhelming lead . She was ahead of Sanders by single digits in polling from a couple weeks ago. Warren was around the threshold. They're the only candidates likely to get delegates out of Minnesota.

Colorado

Delegates at stake: 67
Polls close: 9 p.m. ET

This is one of the three states where Latinos could make a difference. Colorado switched from a caucus to a primary and no entrance polls in 2016, so who will turn out is a bit of a wild card. The state party estimates that Latinos could be as many as 1-in-5 voters.

The very limited polling in the swing state that now leans blue shows Sanders with a lead and Warren the only other candidate above threshold. But the poll was taken before South Carolina, and with Buttigieg out, it's possible Biden ekes out some delegates.

Remarkably, Bloomberg has spent almost $10 million on ads in this state and could get shut out of any delegates.

Tennessee

Delegates: 64
Polls close: 8 p.m. ET

This is the state where Biden has invested most in ads on Super Tuesday (even though it's only $157,000 and is less than half of what Sanders has put in).

There's a reason for that — roughly a third of state's Democratic electorate was black in 2016.

Biden is hoping to run up the score here, especially with wealth venture capitalist Tom Steyer out of the way. Steyer, who was competing for black voters, spent $600,000 on ads in Tennessee. Steyer dropped out after finishing third in South Carolina with just 11% and no delegates after spending almost $24 million on ads there.

Alabama

Delegates at stake: 52
Polls close: 8 pm. ET

This is the most heavily African American Democratic electorate of Super Tuesday. More than half of Alabama Democrats in the 2016 primary were black. Biden hopes to run up the score here and perhaps deny any other candidate delegates.

Oklahoma

Delegates at stake: 37
Polls close: 8 p.m. ET

This state has the highest share of white voters without a college degree of any of the Super Tuesday states. They accounted for more than a third of Democratic voters in the 2016 primary. It's a group Sanders has done well with during the first four contests this year. And in 2016, he won the Oklahoma primary by 18 points over Clinton.

Biden showed improvement with white voters without a college degree in South Carolina. He has to hope to do better with them and that black voters, who accounted for 14% of the 2016 primary electorate, give him an overwhelming margin.

There has been very sparse polling. The latest, conducted about two weeks ago and before the Las Vegas debate, showed Biden statistically tied with Bloomberg, who has spent a whopping $5.3 million in the state. Sanders was teetering on the threshold line.

Warren was below the threshold line; it would be pretty remarkable if she gets no delegates from the state where she was born and raised.

Arkansas

Delegates at stake: 31
Polls close: 8:30 pm ET

Arkansas cuts a similar profile to Oklahoma, but it had a higher share of the electorate that was black in 2016 — 27% of Arkansas Democrats were black, and 34% were whites without a college degree.

There was one poll at the beginning of February, again before the Las Vegas debate, that showed Bloomberg and Biden statistically tied with about a fifth of the vote, and Sanders and Buttigieg around the threshold line. A lot will likely change from that.

Utah

Delegates at stake: 29
Polls close: 10 p.m. ET

The Utah Democratic Party estimates that Latinos account for 14% of the party in this very white state. A poll from last week has Sanders ahead with 28%, Bloomberg at 19%, Warren 15% and Biden below the 15% threshold for delegates. The poll was conducted after the Las Vegas debate, but Bloomberg showed up in the state the day after that debate.

It was Bloomberg's second in-person trip there , and campaigns will tell you, there's no more valuable thing during a campaign than a candidate's time.

Maine

Delegates at stake: 24
Polls close: 8 p.m. ET

Maine is the whitest state to vote on Super Tuesday — the state party estimates that 96% of the party is white. Sanders, the New Englander, led in a poll conducted the second week of February with about a quarter of the vote, followed by Buttigieg and Bloomberg.

Where does Buttigieg's support go now that he's out of the race? It could very well go to Warren, who was competing with him for white voters with college degrees. Biden was slightly below the threshold, making this another state where Biden could get shut out.

Vermont

Delegates at stake: 16
Polls close: 7 p.m. ET

This is Sanders' home state. He's the overwhelming favorite to pick up all 16 delegates here as he did in 2016 .

NPR news assistant Elena Moore contributed to this report.

Copyright 2020 NPR. To see more, visit https://www.npr.org.