Sen. Bernie Sanders Bernard (Bernie) SandersSenate Dems seek to turn tables on GOP in climate change fight Bernie Sanders Town Hall finishes third in cable news race, draws 1.4 million viewers Woman to undecided Biden: 'Just say yes' to 2020 bid MORE (I-Vt.) defended running for president without the aid of a super-PAC to Stephen Colbert on Friday evening, telling the “Late Show” host he’s ginning up plenty of grassroots support without one, according to reports.

“If you want to win it, sir, you’ve got to be in it,” Colbert said. “Every tool in the chest. Don’t bring a spoon to a knife fight.”

ADVERTISEMENT

Sanders responded: “I don’t support the agenda of corporate America or the billionaire class. I don’t want their money.”

“That’s called a people’s campaign, not a billionaire’s campaign,” he added.

Even Colbert acknowledged that crowd sizes at Sanders events have been impressive.

“A guy in his 70s filling stadiums. Who does he think he is? A Rolling Stone?” he quipped.

The socialist senator again went after the GOP front-runner, Donald Trump Donald John TrumpREAD: Cohen testimony alleges Trump knew Stone talked with WikiLeaks about DNC emails Trump urges North Korea to denuclearize ahead of summit Venezuela's Maduro says he fears 'bad' people around Trump MORE, for his controversial remarks on immigration.

“I think that what Trump is doing is appealing to the baser instincts among us — xenophobia, and frankly, racism — describing an entire group of people, in this case Mexicans, as rapists or criminals. I think that’s disgraceful, and not something we should be doing in 2015,” Sanders said.

Sanders rejected comparisons to 2008 candidate Ralph Nader, saying his rising polling numbers and huge rallies indicate genuine momentum, not just a bump in the road for his leading competitor for the Democratic nomination.

“If you look at the polls, we do almost as well … as Hillary Clinton Hillary Diane Rodham ClintonREAD: Cohen testimony alleges Trump knew Stone talked with WikiLeaks about DNC emails County GOP in Minnesota shares image comparing Sanders to Hitler Holder: 'Time to make the Electoral College a vestige of the past' MORE,” Sanders said, "and that will only get better in the future.”