Former Vice President Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE on Friday slammed President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE in one of his most stinging rebukes of the president, saying at a campaign rally that Trump was “trashing American values.”

“He is just trashing American values the way he talks about people, the way he makes fun of people, the way he denigrates folks,” Biden said at a rally in Owingsville, Ky., according to The New York Times. “I got to tell you, I think there is a method to his madness because he wants you to get down in the mosh pit with him.”

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Biden's remarks came as he stumped for Democratic House candidate Amy McGrath.

McGrath faces a tough challenge from GOP Rep. Andy Barr Andy BarrReclaiming the American Dream Powell, Mnuchin stress limits of current emergency lending programs McConnell holds 12-point lead over Democratic challenger McGrath: poll MORE, who has represented Kentucky's 6th District since 2013. McGrath, a former fighter pilot, is running in a district President Trump won by more than 15 points. Still, nonpartisan political handicapper The Cook Political Report has rated the race a "toss-up." Trump is scheduled to campaign for Barr on Saturday.

“We can’t possibly in my view win the presidency unless we can begin to reclaim those white working-class voters that used to vote for us,” Biden told the Times after the rally, adding that he thought Trump's appeal to such voters was limited.

“His value set is much too narrow and self-serving, and I think it’s deliberately designed to appeal to the legitimate frustrations of a lot of working-class people by finding a scapegoat, the ‘other,’ ” Biden added. “Your lost your job, your identity is being threatened because of that immigrant. It’s an old, old method.”

“I look out there and I just don’t know how much more grievance can be appealed to by this guy to keep a majority,” he said.

Biden, who has been seen as a potential front-runner for the Democratic nomination in 2020, said Wednesday that he is not a candidate for his party's presidential nomination "at this point."

"I think there are many people in the Democratic Party who can defeat Trump," he said. "And not a single aspiring candidate that I can think of for the nomination — and I am not one at this point — does not have a better understanding and formulation of American foreign policy than President Trump, in my view."

Biden and Trump have sparred frequently in recent years. The former senator said in March that he would have "beat the hell out of" Trump in high school over his degrading comments about women, later saying that he regretted making the comment.

Trump, last week, said at a campaign-style rally in Kansas that if he fought Biden "it would not last long."

“Remember he challenged me to a fight. ‘I’d like to take him behind the barn.’ I’d love that. That wouldn’t last long. That would not last long. That wouldn’t last long,” the president said, imitating Biden.