Actor Mark Ruffalo, a supporter of Bernie SandersBernard (Bernie) SandersO'Rourke receives invite to visit Iowa from Democratic Party in Des Moines Senators return to Washington intent on action against Saudis Bernie Sanders: 'We have a president who is a racist' MORE, praised the Vermont senator late Sunday after Sanders clashed with Hillary ClintonHillary Diane Rodham ClintonMeet the lawyer Democrats call when it's recount time Overnight Defense — Presented by Raytheon — Mattis defends border deployment during visit to troops | Bolton aide exits WH after clash with first lady | House blocks Yemen war resolution | Report warns of erosion in US military superiority Exit polls show more women breaking with Republicans 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 TrumpMeet the lawyer Democrats call when it's recount time Avenatti denies domestic violence allegations: 'I have never struck a woman' Trump names handbag designer as ambassador to South Africa 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.