IOWA CITY, Iowa ― The political fortunes of former Vice President Joe Biden and Vermont Sen. Bernie Sanders could hinge on how many young voters show up to next week’s Iowa caucuses, which are historically dominated by older voters with the ability to dedicate a full night to participating in the lengthy, labor-intensive process.

Polling in recent days has shown wildly divergent results for Sanders and Biden, who are competing with Massachusetts Sen. Elizabeth Warren and former South Bend, Indiana, Mayor Pete Buttigieg to win Iowa. The victor will receive a major boost to their efforts to claim the 2020 Democratic presidential nomination and the right to challenge President Donald Trump in November.

Age has emerged as the crucial dividing line ahead of the Democratic caucuses here, neatly dividing the coalitions of the two septuagenarians in a way education, class and geography do not. Sanders, whose bold agenda includes aggressive plans to wipe out student debt and battle climate change, disproportionately draws support from millennials and members of Generation Z. Biden, who has unveiled more cautious policy proposals, is heavily reliant on the gray-haired. Each is struggling with the opposite demographic. (The coalitions for both Warren and Buttigieg are more consistent across age groups.)

The Sanders campaign bluntly warned their chances of victory are reliant on college students, in particular, showing up to caucus.

“None of these polls mean anything unless we actually achieve our goal of turning out a record number of college students on Monday,” said Bill Neidhardt, the campaign’s deputy Iowa director.

A New York Times/Siena College poll released Saturday morning found Sanders jumping to a substantial lead, earning 25% of the vote, while Buttigeg draws 18%, Biden 17% and Warren 15%. No other candidate earned double-digit support. John Anzalone, the pollster for the Biden campaign, immediately suggested the poll’s sample leaned too young. Nate Cohn, the Times reporter responsible for the poll, noted Sanders would have led even without the inclusion of any 18-to-29-year-old voters.

“This sample has only 24% over the age of [65],” Anzalone wrote. “There could be up to 30% over the age of 65 going to the Iowa caucuses.”

Meanwhile, a poll released last week from the advocacy group Focus on Rural America found Biden with a healthy lead, earning 24% of the vote to Warren’s 18%. Buttigieg drew 16%, Sanders warranted 14% and Minnesota Sen. Amy Klobuchar 11%. Sanders allies have suggested that poll’s sample skewed older.

There are also contrary pictures of whether or not a surge of young voters could happen. A CIRCLE/Suffolk University poll found 35% of Iowans under the age of 35 planned to participate in the caucuses, which would amount to a massive surge from 2016, when just 11% of the same age group caucused.

Win McNamee via Getty Images Democratic presidential candidate Sen. Bernie Sanders of Vermont speaks to Iowa voters at the Ames City Auditorium in Ames, Iowa, on Jan. 25, 2020.

Such a surge would substantially benefit Sanders, who has consolidated younger voters in the state after many considered Warren and Buttigieg earlier in the cycle. The same poll finds him winning the support of 39% of Iowa Democrats under 35, compared to 19% for Warren and 14% for Buttigieg. Biden earns the support of just 7% of younger Democrats, even trailing entrepreneur Andrew Yang.

But J. Ann Selzer, who conducts the state’s definitive poll for the Des Moines Register, said she has yet to see evidence of a surge of new voters.

“We’re not seeing, at this point, a big number of first-time caucusgoers,” she told WNYC’s “Politics with Amy Walter” podcast. “It’s about what it was in 2016.” Selzer did note her poll didn’t pick up on a surge of first-time caucusgoers backing then-Illinois Sen. Barack Obama in 2008 until the final survey, released the weekend before the caucuses.

The generational divide was visible as Sanders and Biden campaigned across Iowa this weekend. Sanders, accompanied by Rep. Alexandria Ocasio-Cortez, drew a 1,200-person crowd on Saturday night in Ames, the home of Iowa State University. Even without Sanders, Ocasio-Cortez and left-wing filmmaker Michael Moore drew 800 people to the University of Iowa’s campus in Iowa City.

On Monday, Biden held events at two different college campuses ― at Iowa and at the University of Northern Iowa in Cedar Falls ― and drew much smaller crowds. His event at Northern Iowa, in particular, had almost no students in attendance.

At the event, a voter questioned Biden about his lack of support from young people: “What’s an old guy like you going to do to get their support?”

Biden responded by noting that while youth turnout may have jumped in 2018, turnout also spiked among voters over the age of 40.

“Your generation is a situation where you’re the least prejudiced, the most open, you’re the best educated, but until recently ― and then thank God, this has changed ― you haven’t been very interested in politics, generally,” he said. “And so now you’re engaged and I’m looking forward to you voting and voting in big numbers. But everyone is voting in bigger numbers as well.”

Carlos Barria / Reuters Vice President Joe Biden speaks at the University of Iowa on Monday night ahead of the all-important Democratic caucuses in the state.

“The fact is you’ve got to be able to represent anyone,” he continued, before finishing with a joke: “It’s also, I’ve found, very difficult to get people to show up on a college campus before 4 o’clock.”

At the event in Iowa City, Biden specifically took questions from students in the crowd, who quizzed him on his plans for climate change and the economy.

Sanders, meanwhile, has continued to remind voters of his long-standing support for expanding Social Security and his plans to bring down prescription drug prices. The Sanders campaign has spent more than $700,000 on a television ad highlighting his willingness to battle pharmaceutical companies, according to data from Advertising Analytics. And Alex Lawson, a Sanders supporter who runs the advocacy group Social Security Works, has made two trips to Iowa this month to pitch seniors in small towns on Sanders’ agenda. (While Lawson has endorsed Sanders, the group he runs has not.)

Although Sanders has been engaged in a high-profile fight in the national press with Biden over their respective Social Security records, J.D. Scholten, an unaligned Democrat making a second bid to challenge Rep. Steve King for a U.S. House seat in Northwest Iowa, is not sure if his particular message on Social Security was breaking through the noise to ordinary voters.

“It’s hard to say because it gets lumped in with so many other issues,” said Scholten, a Sioux City native who is also a former minor league baseball pitcher.

Scholten has seen some signs that the coalition Sanders has promised to awaken of young, working-class and otherwise disengaged voters is starting to tune in as the caucus approaches. He was impressed with the 1,100-person turnout for a rally with Sanders and Ocasio-Cortez in Sioux City on Sunday night.

“I have never seen a political event like that in Sioux City,” he said, noting Ocasio-Cortez helped draw in the area’s growing Latino population.

The Sanders campaign’s strategy of relying on younger and more independent voters, who typically show up less at the polls, carries risks. The number of registered Democrats in Iowa declined relative to this time in 2019, according to data released by the office of the Iowa secretary of state. That means the campaign will have to recruit that many more people to register as Democrats on the day of the caucus.

Biden, meanwhile, had deployed his own millennial congresswoman to campaign in the state. Rep. Abby Finkenauer, who represents the state’s union-heavy northeast, was among a trio of swing-seat Democrats traveling across the state to tout Biden’s ability to win over independent voters and Republicans.

Finkenauer, who is the second-youngest woman ever elected to Congress — Ocasio-Cortez is the youngest — indicated she wasn’t too worried about Biden’s struggles with young voters. After all, Biden had won over a college-age Finkenauer during his last campaign in 2008.

“My grandfather was a big fan of his,” Finkenauer told reporters during a stop in Cedar Rapids. “I went and I listened because I trusted my papaw. And he loved Joe Biden, and so there I was listening to him, and it hit me that this guy gets it, that he actually understands families like mine.”