Democratic voters in California will consider a suddenly reshaped presidential field Tuesday that has largely narrowed to a rivalry between emerging establishment favorite Joe Biden, billionaire Michael Bloomberg and progressive rivals Bernie Sanders and Elizabeth Warren.

California is one of 14 states that will vote on Super Tuesday. It’s the biggest prize by far, with more than 400 delegates at stake. The vote comes a day after Amy Klobuchar and Pete Buttigieg united behind Biden as party moderates look to halt the ascent of democratic socialist Sanders, the leading candidate after contests in Iowa, New Hampshire, Nevada and South Carolina.

President Donald Trump, who lost California by over 4 million votes in 2016, faces only token opposition for his party’s nomination. Meanwhile, a series of contested U.S. House districts are on the ballot that could play into control of Congress in November.

It’s possible the primary could attract about half of the state’s nearly 21 million registered voters. Early voting began in February, and about 22 percent of 16 million mail-in ballots had been returned as of Monday, according to nonpartisan Political Data Inc.

Arguably, no candidate has more at stake in California than the Vermont senator, whose campaign has long seen the nation’s most populous state as a critical early contest and has had droves of volunteers organizing events across the state.

Sanders was on the California presidential ballot four years ago, when he picked up 46 percent of the vote in a losing effort against eventual nominee Hillary Clinton. He’s hoping for a comeback that would be a capstone moment for the state’s progressive wing, and a string of recent polls have shown him with an advantage over his remaining rivals.

But Sanders is also facing unpredictable factors, not least of which is who actually votes. Some of Sanders’ strongest supporters, including young people and Hispanics, tend to be among the least reliable voters. They are trailing other groups in mail-in ballots returned through Monday.

At the same time, moderate Democrats are clearing the field for South Carolina primary winner Biden, fearing that a Sanders ticket could doom the party’s chances in November. Another recent exit from the race: California billionaire Tom Steyer, who stepped out Saturday.

Anyone who already voted for Klobuchar, Buttigieg or Steyer can’t change their vote.

State election rules intended to increase participation make it likely that ballot-counting could continue for weeks in close contests. Another unknown: Bloomberg, the former New York City mayor who has spent tens of millions of dollars in advertising, is on the ballot for the first time on Super Tuesday.

Four years ago, many Sanders supporters were dejected after his defeat and suspicious of an election process they believe tilted unfairly to Clinton. But his volunteer corps regrouped, and a candidate once considered on the political fringe has this year accumulated more delegates than any other Democrat so far.

The swift reordering of the Democratic contest could provide an opening for Biden, who has been slipping in state polls. He might have another hidden advantage: California prides itself on being the birthplace of the next great thing, but in politics its voters sometimes look backward and favor the familiar.

For example, in the 2008 Democratic presidential primary, when much of the nation was lining up with eventual nominee Barack Obama, California delivered a comfortable victory for Clinton, whose husband, Bill Clinton, carried the state in 1992 and 1996.

Biden planned to be back in California Tuesday. Warren, meanwhile, dug in and made her closing California pitch in a heavily Hispanic neighborhood near Los Angeles, where she told the story of Latina janitors who organized and fought for better working conditions three decades ago.

She drew an immediate contrast with Biden, saying nominating a “Washington inside will not meet this moment.” While she didn’t mention Sanders by name, she offered herself as the progressive who can get things done.

Tulsi Gabbard, who has lagged badly in early contests, also remains in the race.

The long-running tension between the Democratic Party’s progressive wing and its center-left establishment has defined the presidential contest again, as it has for years in many races in California. A Sanders victory would signal a continuing shift to the political left in which voters embrace his “revolution” that includes tuition-free college, breaking up big banks and revamping an economy that has produced a yawning divide between the very wealthy and workaday Americans.

The big change from 2016?

Sanders has made inroads with people of color, especially Hispanics, Sanders pollster Ben Tulchin said. In Nevada, support from Latinos, black people and union members, among others, helped him handily win the caucuses.

“We’ve put together a multiracial, diverse coalition that is putting Bernie in a strong position” to win California and a trove of delegates, Tulchin said.

California delegates are partly divvied up in what amounts to 53 separate elections in congressional districts. A candidate must win 15 percent of the vote in a district to qualify for at least one delegate.

Sanders has pushed back against suggestions that his agenda is pulling the party too far from the center.

“I don’t think so, I honestly don’t,” the Vermont senator told California Democrats at a convention last year.

Progressive activist and Sanders supporter Joe Macaluso said the senator’s strong standing in the state was the culmination of years of political organizing. The result: a broad grassroots movement that’s battle-tested from the 2016 campaign.

“This is a group of experienced activists and organizers in California that … money can’t buy,” Macaluso said.