Transcript for How Bernie Sanders Started a Revolution

Test Text1 underline With his thick Brooklyn accent and his quirky professorial manner, Bernie sanders is the unlikeliest of candidates igniting political revolution. The stage set in New Hampshire for an intense battle between the Vermont senator and the political heavyweight, Hillary Clinton. Here's ABC's David Wright. ? You say you want a revolution ? Reporter: At the stage door of the old colonial theater in Keene, New Hampshire, the fans are gathering. ? You can't buy Bernie ? Reporter: Here as they would put it to feel the Bern. Feel the Bern! Reporter: Bernie sanders' campaign is on fire right now. Front-runner to win the new Hampshire primary -- If you want a government that represents all of the people and not just a few, come on board the political revolution! Reporter: And but for the flip of a coin or two -- he came awfully close to winning the Iowa caucuses too. Tails. It looks like we are in a virtual tie. Reporter: The 74-year-old junior senator from Vermont, the only democratic socialist in congress, now giving Hillary Clinton a serious run for her money. His campaign raised $3 million in 24 hours after Iowa. Integrity and authenticity are words his supporters use. Feels good to have somebody around that feels worth getting passionate about. There are a lot of conversations that he's presenting that we need to be having in this country. Bernie talks about attacking the corrupt campaign finances, he talks about raising the minimum wage to a living wage, he talks about bringing back manufacturing, he talks about infrastructure. Reporter: A political rise nobody but Bernie saw coming. When I first met him a year ago, he was just considering whether to throw his hat into the ring. Would you be in it to win it or in it to articulate positions? That I know the answer to. If I ran, I would run to win. I know if I do this, I start off as a significant underdog. 70% of the American people don't know who Bernie sanders is. The word snowball's chance comes to mind. No offense. Reporter: He's out there raising fundamental questions about the American political system and the U.S. Economy. A system he says is rigged in favor of billionaires and bankers. We the people are going to have to have a government that represents all of us, not just a handful of billionaires. Reporter: He rails against the 1% and the politicians they keep in their pocket. His platform straight out of occupy Wall Street. College education free-for-all Americans. Health care free for all Americans. He'd break up the big banks, raise the minimum wage, and fund all this by raising taxes on the rich and on corporations. Are you tilting at wind mills? Or do you think this is a minutable fight? I don't want to tilt at wind mills. There are so many people who are hurting, working longer hours for low wages, and the billionaires are getting richer. They need a voice. Reporter: Bernie sanders has given them a voice. And he's put his money where his mouth is. There's no super pac aligned with his campaign. Instead, he's funding it with record Numbers of small donations. 3.25 million of them. Average amount $27 apiece, according to his campaign. He's an unlikely messenger, easily parodied by "Snl" -- The other candidates are taking millions from the coke brothers and ExxonMobil. But not me. I only accept coins. I'm not talking about fancy coins like dimes and quarters. I just want nickels and pennies. Reporter: His main campaign ad features a golden oldie. ? Look for America ? Reporter: Simon and Garfunkel with an upbeat message. His events you find plenty of folks from the woodstock yes or no race. I am feeling the Bern! Reporter: Also legions of younger voters. Feel the Bern! Reporter: Among registered democrats aged 29 and younger, nationally sanders outpolls Clinton nearly 4-1. I just like his ideas for Wall Street and what he's going to do with our future education. It's already been incredibly impressive for him. Reporter: Digital journalist Mary Alice parks has been traveling with the sanders campaign for months. It has been huge since the beginning. The biggest crowds were over the summer in a west coast swing, 28,000 people in Portland, almost 25,000 in L.A. Very reminiscent of Obama. Big change, high hopes, high dreams. Reporter: Sanders has pledged to fight a clean campaign, even refusing to attack Clinton's use of a private e-mail server. The American people are sick and tired of hearing about your damn e-mails. Thank you. Me too. Me too. Reporter: Now he's drawing sharper distinctions. Hitting her hardest on her ties to Wall Street and her dependance on campaign contributions. Do you think Hillary Clinton is a Progressive? Some days, yes. Except when she announces that she is a proud moderate. Then I guess she's not a Progressive. It was kind of a low blow. Reporter: Today here in new Hampshire, Clinton fired back. It was a good day for Progressives when I helped to get 8 million kids health care under the children's health insurance program. Reporter: The lowest polls show Clinton trailing sanders by more than 20 points here. Clinton and others chalk that up to the fact he has the home court advantage as the senator from a neighboring state. Tonight he reminded voters at a CNN town hall that Hillary Clinton voted for the Iraq invasion. He didn't. The Progressive community was pretty united in saying, don't listen to bush, don't go to war. Secretary Clinton voted to go to war. Reporter: Obviously you still haven't gotten the memo, this was supposed to be a coronation, right? No, we didn't get that memo. Reporter: What's not yet clear is whether Bernie sanders is a new and improved version -- Yes, we can! Thank you, New Hampshire! Reporter: -- Of the force that came out of nowhere back in 2008 to take away Hillary's crown. Eight years ago Barack Obama was here. He talked about, yes, we can. Yep. Let's be honest on a lot of things he just couldn't. What makes you think you can? People are tired of a rigged economy and a corrupt campaign finance system. They want real change. That's why we're doing well. Reporter: Back outside the colonial theater, there's no question they're feeling the Bern. I feel the Bern! Whoo! Reporter: I'm David Wright for "Nightline" in Keene, new Hampshire. As for the republicans, you do not want to miss the last republican debate before the new Hampshire primary Saturday night right here on ABC.

This transcript has been automatically generated and may not be 100% accurate.