But if there is high turnout in Iowa, he said, “It may help the other candidates: It may be what they need to stay viable.”

The Iowa Democratic Party has been preparing for record-breaking turnout for more than a year, driven both by Democrats’ angst about President Donald Trump and by an unusually large field of candidates — many of them with their own significant, independent turnout operations. The state party chairman, Troy Price, said the party is anticipating more caucus-goers than in 2008, which set a record when 239,000 Democratic voters participated, lifting Obama to victory.

“The winner is always who’s bringing a bunch of new [voters], said Sue Dvorsky, a former Iowa Democratic Party chairwoman who backed Sen. Kamala Harris before she dropped out of the race.

The difficulty this year, she said, is that new voters could go to any number of different candidates. “There literally is no historical analogy here,” she said.

Every candidate could see potential advantages in a high-turnout caucus. And the weekend saw each of them working furiously to swell their lanes of support.

Sanders, whose effort to mobilize young voters in 2016 helped him nearly upset Hillary Clinton in Iowa, exhorted an overflow crowd in Ames, Iowa on Saturday “to bring your friends and your co-workers and your fellow students and your moms and your dads and everybody else out.”

“Because I will tell you this without a shadow of a doubt,” Sanders said. “If there is a large voter turnout — if working people and young people come out in large numbers — we will win and win big.”

A poll by the The New York Times/Siena College on Saturday put Sanders ahead of the field in Iowa with 25 percent support, followed by Buttigieg at 18 percent, Biden at 17 percent and Warren at 15 percent.

That same day, Sanders, Rep. Alexandria Ocasio-Cortez and filmmaker Michael Moore spoke to more than 1,400 people in Ames, according to his campaign. Mentions of Sanders on Twitter from Iowa were up 62 percent in the past two weeks, with a total outpacing every other candidate, according to an analysis conducted for POLITICO by the media intelligence company Meltwater.

“If there's a huge voter turnout, you can turn off your TV — Bernie won,” Sanders spokesman Mike Casca said in an email.

But Biden still leads Sanders in national polling, and he is running about even with him in Iowa, according to the Real Clear Politics polling average. Large turnout could benefit Biden if Klobuchar, a lower-polling centrist, fails to meet the 15 percent threshold necessary to win delegates in Iowa precincts. Many of her supporters are expected to shift allegiance to Biden if she does not hit that threshold.

“If the surge is younger, you have to think it helps Bernie and maybe Warren,” said Jeff Link, a Democratic strategist in Iowa. “If older Democrats and independents decide it’s worth participating this time, it probably helps Biden and maybe Buttigieg.”

Campaigning with Biden in Iowa on Sunday, Rep. Abby Finkenauer asked every voter she met if they were planning to caucus. For those with children, she queried whether they would bring them along as observers or volunteers.

“I can’t predict what it’s going to look like that night,” Finkenauer said. “Who knows if the weather will have something to do with it. I’ve been joking with people [saying], ‘We need to get snow mobiles.’ I don’t know. But things feel really good on the ground here. Folks are engaged and excited.”

A senior adviser on Biden’s campaign pointed to rural areas of the state, saying a bigger draw there could potentially benefit the former vice president. The person noted that the campaign has targeted Republicans, independents and those who don’t identify with any party to participate in the caucus.

Because registration is allowed on caucus day, the caucuses could draw independent voters and even some Republicans who are turned off by Trump. Moderate Democrats are actively working to turn out those potential voters.

"We’ve been proactive engaging Republicans to participate in the caucus," the adviser said.

Buttigieg is also courting Republicans and independents, while sounding alarms about Sanders. His campaign issued a fundraising email on Saturday with a not-so-subtle subject line: “Bernie Sanders could be the nominee.”

“I think that the higher the turnout, the more people that are participating, it’s going to be better for us,” said a senior adviser with Buttigieg’s campaign. “We want new people, we want Republicans, we want independents. We encounter a lot of Trump voters and a lot of Republicans, who want to be involved. I think we’re going to have real crossover appeal.”

Buttigieg’s appeal to potential swing voters, the campaign argues, is evidenced by the geographic areas of the state where he has held events and drawn large crowds.

Still, another Buttigieg adviser acknowledged that the spoils of high turnout could be split fairly evenly among the current top tier of candidates.

“It’s not like 2016, where you have the most establishment running against the most anti-establishment candidate,” the adviser said.

The caucuses will be an enormous test for Warren and Buttigieg’s field operations, which have impressed Democratic activists in the state for months.

Sean Bagniewski, chairman of the Polk County Democrats, said Buttigieg’s campaign recently drew about 300 people to a training for precinct caucus captains, enough for multiple precinct captains at some caucus sites next week. Warren has assembled such a vast army that her campaign is helping Bagniewski fill caucus chair positions at its caucus sites, he said.

“The fact that they have bandwidth to be helping the county party means they’re pretty damn organized,” he said.

A lower turnout election is still possible, and the lack of a spike in Democratic voter registrations has caused some observers to temper expectations.

But two strategists familiar with campaigns in Iowa said multiple campaigns were urging supporters in at least some areas of the state not to register until the day of the caucuses — a ploy to prevent other campaigns from targeting them ahead of caucus day.

Chris Adcock, chairwoman of Democratic Party in Page County in southwest Iowa, said that if turnout is low, “I think [the beneficiaries] would be Sanders and Biden, because they are known quantities.”

But Adcock, like most activists in Iowa, expects turnout to be high. She has added caucus sites in her county, and she said Klobuchar and Warren’s campaigns could be rewarded next week for months of “working really hard.”

Organizers of a caucus site in Ankeny, just north of Des Moines, said they are expecting 100 to 150 more people to caucus Monday than did in 2016. And further west in tiny Audubon County, Sarah Christensen, a caucus chair, said of high turnout projections, “That’s what they say.”

“The Iowa Democratic Party sent me 200 caucus cards, and we've requested more,” she said. “I don't know if we'll need them, but I get the sense that we might.”

Holly Otterbein contributed to this report.