Actor Mark Ruffalo, a supporter of Bernie SandersBernard (Bernie) SandersPollster: Despite flashy headline, Dems haven't become more supportive of socialism Pollster: Dem party 'rift' won't carry on to midterms Pelosi sees defections from an unusual quarter — the left MORE, praised the Vermont senator late Sunday after Sanders clashed with Hillary ClintonHillary Diane Rodham ClintonPapadopoulos's wife wants him to scrap plea deal with Mueller: report FBI chief: I'm trying to bring 'normalcy' in 'turbulent times' Senate Intel chief slams ex-CIA director for timing of claims about Trump-Russia ties MORE in the latest Democratic presidential debate.

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"He was charming, he was direct, he felt fresh in his answers," Ruffalo said in a post-debate appearance on MSNBC. "I just felt a lot of heart from him."

"He awoke something in me, and it was his ideas, and it's his decency, and it's his record, frankly," Ruffalo added.

"This guy is exactly who he's always been, he's always been fighting for the little guy, and today that just happens to be the very person we need," Ruffalo said.

"There's an authenticity about him and about his history and about his career as a politician that speaks to me."

Sanders and Clinton tangled on the auto industry and water during the debate Sunday night held in Flint, Mich., which has been under the national spotlight for months over its water contamination crisis.

Both Democratic candidates called for the state's Republican governor, Rick Snyder, to step down and be held responsible for the situation. They also weighed in on accountability for Environmental Protection Authority officials.

Ruffalo, an anti-fracking activist, was also active on Twitter on behalf of Sanders, saying that Sanders was "crushing it" at the debate while stating that "Clinton supports fracking" while Sanders "does not."

The actor also weighed in on the possibility of Sanders facing off against Republican presidential front-runner Donald TrumpDonald John TrumpNFL players stand in tunnel during anthem, extending protests 12 former top intel officials blast Trump's move to revoke Brennan's security clearance NYT: Omarosa believed to have as many as 200 tapes MORE in the general election.

"There's no doubt in my mind he could beat Donald Trump if he goes up against him," Ruffalo told MSNBC, adding that he thought the self-described democratic socialist would "mop the floor" with Trump.