What is Super Tuesday and why does it matter?

Super Tuesday is a significant day in the presidential primary race -- when 16 states total, plus the territory of American Samoa, head to the polls.

While the presidential contest will receive a good amount of the attention, there are several significant down-ballot races as well since some states hold other primaries on the same day.

Here's what to know about Super Tuesday.

What happens on Super Tuesday?

Super Tuesday -- a tradition that traces back decades, which will be held this year on March 5 -- is notable in the presidential race because it has the most states voting simultaneously and the most delegates up for grabs in the nominating calendar, more than one-third of the total for each party.

That could bring both former President Donald Trump and President Joe Biden significantly closer to clinching their respective nominations. Trump faces former South Carolina Gov. Nikki Haley while Biden is running against long shot challengers Rep. Dean Phillips and Marianne Williamson.

The 16 states that will vote on Super Tuesday are Alabama, Alaska, Arkansas, California, Colorado, Iowa, Maine, Massachusetts, Minnesota, North Carolina, Oklahoma, Tennessee, Texas, Utah, Vermont and Virginia.

However, Alaska will only vote on Republican candidates and Iowa is only voting on Democratic candidates.

One territory, American Samoa, will cast ballots in the Democratic race as well.

State polls close at various times beginning at 7 p.m. EST and going until 12 a.m. EST when voting ends in Alaska's Republican contest. ABC News and 538 will have Super Tuesday results, takeaways and analysis throughout the night.

Where do things stand in the GOP presidential primary?

Former U.N. Ambassador Haley will continue her effort to topple former President Trump, the front-runner -- however, after a series of big losses so far (except in Washington, D.C.), it's expected to be tough for Haley to eke out a win in any of the states on Super Tuesday.

That's because she remains behind in the polls tracked by 538. For example, she trails Trump by more than 60 points, according to the latest 538 national average.

Tuesday's outcome could signal the end for Haley, too.

On Friday, she hinted that decisions beyond Super Tuesday will be based on whether she's still "competitive" in primaries and caucuses, while not defining exactly what that would look like.

Haley earned 27% of the GOP vote in Michigan last week and argued that showed a substantial minority of the Republican Party doesn't want Trump at the helm even though he keeps winning.

Trump, however, said his win in Michigan was "far greater than anticipated." He likewise insisted after winning South Carolina with 60% of the vote that "I have never seen the Republican Party so unified."

Both he and Haley have been campaigning across Super Tuesday states, speaking with voters about why they should be the next commander in chief. Last week, Trump visited Texas the same day as Biden, where both discussed border policy and high immigration numbers, a major campaign issue.

How many delegates are at stake?

Super Tuesday marks the day when the most delegates are at stake in the presidential primary -- and strong performances from Biden and Trump could help them get closer to their party's nomination.

On the Republican side, 865 delegates are in play out of the 2,429 total delegates. To clinch the nomination, 1,215 are needed.

California and Texas have the heftiest number of delegates with 169 and 161, respectively.

On the Democrats' side, 1,420 delegates are up for grabs of the 3,934 pledged delegates awarded as part of the primary process. Biden would need 1,968 to earn the nomination.

California holds the most weight with Democrats, with a whopping 424 delegates.

While both Biden and Trump will work to earn the delegates, neither will be able to lock in the nomination on Super Tuesday.

What about other races?

Outside of the Republican presidential primary contest, there are several down-ballot races that are getting a lot of attention.

In California, there is the primary for the Senate seat to replace Sen. Dianne Feinstein, who died last fall. The four leading contenders are Democratic Reps. Adam Schiff, Katie Porter and Barbara Lee, plus Republican Steve Garvey, a former Major League Baseball player.

In North Carolina, the contest to be the next governor is taking shape with clear front-runners in both the Democratic and Republican primaries. For the GOP, it's Lt. Gov. Mark Robinson, an Army veteran and devout Christian. The front-runner for the Democrats is Attorney General Josh Stein, who has raised more funds than any candidate on either side.

In Texas, Democrats are again trying to unseat Sen. Ted Cruz -- and nine candidates are running for the chance. The front-runner is Rep. Colin Allred, a former NFL player and civil rights attorney who has represented the Dallas area since 2019.

What's next?

After Super Tuesday, the GOP presidential primary will continue on with American Samoa's contest on Friday and then four more states holding races on March 12, followed by five more on March 19.

538's Kaleigh Rogers and Geoffrey Skelley contributed to this report.