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 on Wednesday downplayed the threat posed by 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 as a possible Democratic opponent in 2020.

"He’s a sleepy man, but I just don’t know," Trump said of Biden in an interview with Boston Herald Radio when asked which Democratic presidential candidates he fears. "I mean, who knows really who can do the best? In many ways, I like him."

Trump’s team views Biden as a strong 2020 contender if he can secure the Democratic nomination, and the president has gone after the former vice president in order to diminish his standing, even as his campaign has largely held its fire against specific Democratic opponents.

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Many in Washington view Trump’s attacks as a sign he is worried about a potential run against Biden, but the president predicted that "we’re going to do great."

"He’s not as smart as Bernie, and he’s not as quick," Trump said of Biden, comparing him to Sen. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.), another top-tier Democratic primary candidate.

The president acknowledged Biden has "different views a little bit" from the rest of the Democratic primary field but said he believes "they’re all pretty heavy leaning left, including him."

Trump again railed against the decision of the International Association of Fire Fighters to endorse Biden, claiming without evidence "there was outrage by firefighters" at the decision.

"They’re for me. I mean, firefighters are going to be voting for me. So are the police. So are the military. These are all people voting for me," Trump said, calling union leaders "dues-sucking people" who have reflexively supported Democrats for decades.

Trump on Wednesday morning went on a Twitter spree, retweeting nearly 60 messages voicing support from rank-and-file firefighters.

Biden’s campaign strategy centers on winning back white, working-class voters who largely defected from the Democratic Party in 2016 and helped propel Trump to the White House.