For two hours Saturday at the University of Iowa, the mostly college-aged crowd of kids with asymmetrical haircuts and baggy denim waited for the 74-year-old headliner, Bernie Sanders.

In the mean time, they screamed for Hunger Games heartthrob and Sanders supporter Josh Hutcherson, swayed to the sensitive folk rock of Mark Foster and went wild for indie-pop mainstays Vampire Weekend.

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A Bernie Sanders supporter at a youth rally and concert at the University of Iowa in Iowa City holds up a campaign sign on Saturday. (Matt Kwong/CBC)

"This is dope," said Michael Lichtenberger, 21, standing about three metres from the empty lectern.

"Feel the Bern, 2016!" added Alicia Freiburg, 20, quoting the Democratic presidential candidate's rallying cry.

It seemed it would be a fun pre-caucus opener for the crowd of about 3,000 people.

Then the senator from Vermont stepped onto the riser. He had some troubling things to share.

"What this campaign is about is very, very serious business," Sanders began.

Clinton 'déjà vu'

For the next half hour, the self-described Democratic Socialist unpacked a litany of problems contributing to his disillusionment with America, excoriating the billionaire class, the justice system, and railing against man-made climate change and institutionalized racism.

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U.S. Democratic presidential candidate Bernie Sanders speaks at a campaign rally and concert at the University of Iowa in Iowa City, Iowa, on Jan. 30, 2016. (Mark Kauzlarich/Reuters)

A bummer? Not for the roomful of millennials, a demographic with which Sanders has taken an edge over Democratic rival Hillary Clinton, once considered the "inevitable" candidate.

"Bernie! Bernie!" they cheered, intermittently drowning out the candidate's words.

What might have seemed unthinkable even six months ago — that Clinton's Democratic coronation would be at risk — now looks worrisome for the woman vying to be the first female commander in chief.

It's laid bare in the latest Iowa Quinnipiac poll: Sanders with 78 per cent favourability among voters aged 18-44; Clinton holding 21 per cent of the same key age group.

To pundits, it's a bit of a flashback.

No presumptive nominees

"Hillary Clinton's Iowa déjà vu," ran a headline on Politico analyzing Sanders's surging momentum, comparing her situation to the 2008 upset when Barack Obama, then a relatively unknown senator from Illinois, ended up commanding the youth vote and prevailing in the Hawkeye state.

"To think that we can take Iowa? There's so much power in that," said Canadian Linh Nguyen, 28, who left Toronto and moved to Des Moines in December to work for the Sanders campaign. "We're pushing for a political revolution, what could be one of the biggest political upsets in recent U.S. history."

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Pundits say U.S. Democratic presidential candidate Hillary Clinton's status as a presumptive nominee is now in question as her chief rival, Bernie Sanders, draws large crowds of young voters and narrows the gap in Iowa among likely Democratic caucus-goers. (Adrees Latif/Reuters)

If this election cycle has taught us anything, it is there are no presumptive nominees, says Amanda Loutris, 17.

"[Clinton] is not the untouchable candidate they thought she is," said Loutris, who graduated a semester early from high school so she could dedicate more time to campaigning for Sanders in Des Moines.

"Bernie's got a real shot."

Clinton still maintains a lead in Iowa polls, but the gap has narrowed. The final Des Moines Register poll before the caucuses on Feb. 1 placed Hillary just three points ahead of Sanders overall among likely Democratic caucus-goers, with 45 per cent support to 42 per cent for Sanders. Former governor of Maryland Martin O'Malley was a distant third place, with three per cent favourability.

Around the Field House concert venue in Iowa City, young people said that a commitment to introducing single-payer health care, free public college tuition and a plan to overturn Citizens United — the 2010 Supreme Court decision that let big money seep into election funding — drew them to this rally. Sanders was merely the vessel to deliver those ideas.

DEM 2016 Sanders

Democratic presidential candidate Sen. Bernie Sanders, left, and Vampire Weekend lead singer Ezra Koenig wave during a campaign rally at the University of Iowa on Saturday. (Evan Vucci/Associated Press)

"It frustrates me how fatalistic some people can be about saying we know Hillary will be the nominee," Luke Stroth, 21, shouted over a din of acoustic folk. "But here in Johnson County at least? Just being in this atmosphere and seeing this crowd, I feel they're going to go for Bernie."

For all its first-in-the-nation prominence, however, Democratic strategist Joe Trippi cautions against reading too much into Iowa caucus outcomes for the party.

Iowa, which is 92 per cent white, only tells part of the story, he says.

"Sanders really excites young people and white progressives. Well, that's two parts of the [Democratic] coalition," says Trippi, who worked on Howard Dean's 2004 Iowa campaign. "You look at Clinton and she beats him when it comes to women, factory blue-collar whites, African-Americans and Hispanics. Her strengths don't exist in Iowa or New Hampshire."

Trippi believes a Sanders victory in the Iowa caucuses may only prove he can split the white Democratic vote in that state, nothing more.

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University of Iowa students, from left, Michael Lichtenberger, 21; Alicia Freiburg, 20; Devin Tracey, 19, and Justin Charvat, 21. All four say they will caucus for Bernie Sanders on Feb. 1 in Iowa's liberal-leaning Johnson County. (Matt Kwong/CBC)

As for the comparisons to the Obama horse race in 2008? Trippi doesn't expect that can be replicated.

"In 2008, Hillary ran against the one person still alive who could overwhelm her with that diverse a coalition," Trippi says. "To think that in 2016, Bernie Sanders will do the same, that's just fantasy."

What remains to be seen is whether Sanders get-out-the-vote volunteers will be able to rally enough new caucus-goers to support him. A large turnout could put the thumb on the scale.

All that aside, the allure of Sanders did appear to be pan-generational. Some silver-haired seniors attended Saturday's youth rally and concert, and it was a family affair for Joel Wells, 69, and his son Keegan, 29.

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Joel Wells, 69, and his sister Susan Dennemy, 53, were among a few non-millennials to attend a rally and concert for Bernie Sanders on Saturday in Iowa City. (Matt Kwong/CBC)

Wells, a heavy-equipment inspector, may not have cared much for indie-pop star Mark Foster's plaintive crooning on the concert stage, but he believes enough in Sanders to be a precinct chair for the campaign.

"Bernie believes in making some justice out of the American system, where the top one per cent is making an ungodly amount of money and the rest of us don't make anything," he said.

"The band's fine, but I came for Bernie."

DEM 2016 Sanders

Jane Sanders, right, looks on as her husband Democratic presidential candidate Sen. Bernie Sanders, pumps his fist during a campaign rally at the University of Iowa, on Saturday. (Associated Press)