Sen. Bernie Sanders took to Twitter on the evening of the momentum-building Iowa Caucuses to make a final appeal to potential supporters after telling a Des Moines bar hosting a Super Bowl party that the caucuses represented the "beginning of the end for Donald Trump."

Sanders made his appeal while he appears to be either leading in polls in the state or near the top.

"So, tomorrow night is the beginning. It is the beginning of the end for Donald Trump,” Sanders said. "At the beginning of the moment when we tell the billionaire class in the 1 percent: this country belongs to all of us, not just a few."

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There is reportedly some concern in the Democratic Party about the possibility of the self-described democratic socialist becoming the party’s standard-bearer. Hillary Clinton has recently been a harsh critic of her former opponent and last week claimed that Sanders did not do enough to help her unite the party in 2016 after she won the primary.

Sanders' supporters are known for their loyalty, but much of his success in 2020 will hinge on whether or not he can broaden his appeal.

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"By joining our movement, you're joining a fight for human solidarity," he tweeted. "You're standing against all forms of racism, bigotry and discrimination. You're working towards criminal justice reform, a humane immigration system and disability rights. That’s what this campaign is about."

Perhaps Friday night’s fundraising concert for the Vermont senator illustrates the uneasy relationship the progressive wing of the party has with the moderates. Rep. Rashida Tlaib, D-Mich., according to the AP, led sustained booing from the stage at the mention of Clinton. Rep. Alexandria Ocasio-Cortez, D-N.Y., another Sanders supporter, said the Democratic establishment should conform to the progressive movement, not the other way around.

"We aren't pushing the party left," she said. "We are bringing the party home."

Former Secretary of State John Kerry, who is in Des Moines as a Joe Biden's surrogate, was overheard in a hotel restaurant Sunday warning of the very real "possibility of Bernie Sanders taking down the Democratic Party -- down whole," according to an NBC News report. He reportedly remarked that "maybe I'm f---ing deluding myself here," but that he could conceivably launch a run for president now that donors "have the reality of Bernie" surging in the polls.

He later denied the report in a now-deleted profanity-laced tweet.

Clinton, for her part, also made news earlier in January when she told The Hollywood Reporter "nobody likes" Sanders. "Nobody wants to work with him, he got nothing done," she claimed.

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She at first didn’t say if she would support him if he were the nominee, but later responded to a backlash, clarifying she’ll do whatever she can to “support our nominee.”

Fox News’ Gregg Re, Brie Stimson and The Associated Press contributed to this report.