US President Donald Trump and former vice president Joe Biden are in a rhetorical fight over which of them would prevail in a brawl.
Mr Trump, reacting to comments Mr Biden made about him earlier in the week at an anti-sexual assault rally, tweeted on Thursday: "Crazy Joe Biden is trying to act like a tough guy.
"Actually, he is weak, both mentally and physically, and yet he threatens me, for the second time, with physical assault.
"He doesn't know me, but he would go down fast and hard, crying all the way.
"Don't threaten people Joe!"
At the University of Miami on Tuesday, Mr Biden cited lewd comments the Republican president made in a 2005 Access Hollywood tape about grabbing women without their permission.
"If we were in high school, I'd take him behind the gym and beat the hell out of him," said Mr Biden, a Democrat.
He also said any man who disrespected women was "usually the fattest, ugliest S.O.B. in the room".
Mr Biden, 75, made similar comments in the closing days of the 2016 campaign.
He has kept open the possibility of a 2020 bid for president and is gearing up to play a big role campaigning for Democrats running in this year's midterm elections.
Mr Trump, 71, dismissed the prospect of a Biden run recently at the annual Gridiron Dinner with Washington journalists, calling him "Sleepy Joe" and saying he could "kick his ass".
Mr Trump also attacked Mr Biden on Twitter in 2016, calling him "Our not very bright vice president."
