"I shouldn't say that - (but) there's nothing to be embarrassed about".
Trump's overt praise of a representative physically assaulting a journalist would never be okay, but the timing feels even more precarious given the presumed murder of Washington Post journalist Jamal Khashoggi in the Saudi consulate in Istanbul.
Earlier this year, Biden, who is considering a 2020 presidential bid, said he would have "beat the hell" out of Trump when they were younger.
Trump's comment was a reference to when Gianforte body-slammed a reporter in 2017 who got up in his face. "He's going to lose the election, '" Trump said.
He paid a $385 fine and completed 40 hours of community service and 20 hours of anger management counselling.
His remarks praising Mr Gianforte come amid an global furore over the apparent assassination of Washington Post columnist Jamal Khashoggi, who allegedly had his fingers cut off and was decapitated inside a Saudi consulate in Istanbul two weeks ago.
"The president of the United States tonight applauded the assault on an American journalist who works for the Guardian".
Khashoggi, an outspoken critic of Saudi Arabia and its leader, Crown Prince Mohammed bin Salman, reportedly feared that his native county would retaliate against him.
In a statement, the Guardian's US editor John Mulholland said he hoped the president would apologise for his comments, adding: "To celebrate an attack on a journalist who was simply doing his job is an attack on the first amendment [of the US Constitution] by someone who has taken an oath to defend it".