Actor Mark Ruffalo, a supporter of Bernie SandersBernard (Bernie) SandersSchumer: Franken should resign Franken resignation could upend Minnesota races Avalanche of Democratic senators say Franken should resign MORE, praised the Vermont senator late Sunday after Sanders clashed with Hillary ClintonHillary Diane Rodham ClintonGrassley blasts Democrats over unwillingness to probe Clinton GOP lawmakers cite new allegations of political bias in FBI Top intel Dem: Trump Jr. refused to answer questions about Trump Tower discussions with father 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 TrumpHouse Democrat slams Donald Trump Jr. for ‘serious case of amnesia’ after testimony Skier Lindsey Vonn: I don’t want to represent Trump at Olympics Poll: 4 in 10 Republicans think senior Trump advisers had improper dealings with Russia 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.