Trump, 78, said on Monday that Biden, 81, would refuse to quit the campaign because of his ego and noted that the president had the Democratic nomination locked up because of all the convention delegates he won during the Democratic primary elections earlier this year, Reuters reported.

Biden has repeatedly said he is staying in the race.

"Interestingly, he's got a lot of power, because he's got the delegates. You know, when you have the delegates, unless he says, 'I'm getting out,' they can't do anything to get him out other than the 25th amendment," Trump said.

The 25th amendment of the US constitution enables the vice president and cabinet members to declare the president is unable to discharge the powers and duties of the office, transferring the job to the vice president as acting president. There is no indication Vice President Kamala Harris or top Democrats have advanced that option.

"He's got an ego, and he doesn't want to quit. He doesn't want to do that. It just looks to me like that's what he wants," Trump said of his rival, who unseated Trump when the former president ran for re-election in 2020.