Former Vice President Joe Biden, the frontrunner among 2020 Democratic candidates, agreed with a supporter who blasted Donald Trump's presidency -- and called it "illegitimate" -- during a fiery rant at his latest campaign stop.

"He is an illegitimate president in my mind. That's it," the woman, who said she had "a very severe case of what's called Trump derangement syndrome," told Biden.

"He's illegitimate and my biggest fear is that he's going to do it again with the help of Vlad, his best pal, and we're going to be stuck for six more years with this guy, and that is terrifying, it's terrifying," she said, mentioning Russian president Vladimir Putin.

Biden responded by jokingly asking if she would be his vice presidential candidate. In a seemingly more serious tone, Biden said, "folks, look, I absolutely agree."

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Her comments also included a call for all 2020 candidates to unify behind a message that claimed, among other things, Trump won the 2016 election with Russia's help. "I don't want to live in a country run by Vladimir Putin. I don't think anybody should want that," she added.

Biden told the woman that in order to help Democrats win, he wouldn't "speak ill" of another Democratic candidates. "We have to be in a position, whomever the nominee is, to be able to win," he said.

Biden has a history of making comments potentially damaging to his political career. For example, he told a Chinese university audience in 2011 that he "fully" understood their one-child policy.

The former vice president also faced scrutiny over a 2006 video, resurfaced in May, showing him advocating for a border wall and punishment for employers who hired illegal immigrants.

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Biden's Tuesday comments came after weeks of turmoil surrounding Special Counsel Robert Mueller's report which highlighted what some considered to be troubling activity by Russians. The report did not, however, conclude the Trump campaign conspired with the Russians to influence the election.

While Democrats have continued investigating potential obstruction of justice under Trump, the Justice Department probed the Russia investigation's origins and whether the former administration improperly surveilled Trump's campaign.

Fox News contacted Joe Biden's campaign for comment.