The mobilization of his young army of admirers will help determine whether he's able to slow -- or stop -- Hillary Clinton's
march to the Democratic presidential nomination.
"I have to admit, I'm not the hippest guy around," Sanders told CNN in an interview aboard his campaign bus. "I have to freely admit that."
Yet the 74-year-old Vermont senator has become one of the hippest candidates of the election cycle, at least in the digital world, where he's developed an unlikely following of young supporters.
"Bernie Sanders is America's uncle," Jake Hoyng, 17, who was drawn to Sanders by some of his friends. He intends to caucus for Sanders next Monday in Iowa, which is allowed because he will be 18 by Election Day in November.
It's an open question how many young voters like Hoyng, particularly in the 17-to-25 age range that Sanders is targeting, will take part in the Iowa caucuses. The campaign is trying to rally supporters through a new website
and advertising on Reddit, with a challenge to prove skeptics wrong:
They say you don't care.
They say you won't caucus.
They say Bernie can't win.
Prove them wrong.
As he travels across the country, Sanders' crowds look far younger than that of other candidates, including Clinton's. In Iowa, the contrast is particularly stark, with Clinton drawing far older audiences. But those voters, traditionally, are far more reliable.
The Sanders campaign launched a new push on Snapchat, running daily advertisements encouraging people to attend the caucuses and share their pictures with other supporters. The ads are targeted by geography, with only people in Iowa allowed to put the campaign messages over their photos or video.
"We're leveraging Snapchat to help us turn out young caucus-goers in Iowa who know Sen. Sanders is the best candidate to make college affordable, fight climate change and take on a corrupt political system," said Kenneth Pennington, the campaign's digital director.
Sanders said he had little doubt his supporters would vote.
"Young people are by nature idealistic," Sanders said in an interview. "They understand that something is wrong in this country when our middle class continues to decline and when they may end up with a lower standard of living than their parents. They want us to do something about it."
It's supporters like Kailey Gray, a 20-year-old student at Drake University, who is fueling his rise. She volunteers night and day for Sanders at his headquarters in a crowded strip mall on the north side of Des Moines.
"A lot of young people are turned off by politicians because they don't exactly tell the truth all the time and flip flop around the issues," Gray said. "You can just kind of tell when someone isn't sincere, but Bernie's been saying the same thing for decades and he doesn't sway on the issues. He really knows what's right and sticks to what he believes in even if it's not the most popular."
If elected, Sanders would be the oldest president -- nearly six years older than Ronald Reagan when he took office. He pledged Monday night to release his medical records before the Iowa caucuses.
Sanders has aggressively campaigned on college campuses across Iowa. He often arrives to loud cheers, even after declaring awkward phrases like, "Guess what youngins?"
His wife, Jane, who is often at his side on the campaign trail, marvels at his young following.
"When he was mayor he was popular among young people," she said with a smile. "Hip, I never expected."