Donald Trump mocked Joe Biden for mistakenly calling him "George" during a televised campaign event and accused the US media of helping his Democratic rival "get through" interviews.
Biden was speaking at a virtual concert on Sunday night when he said: "Four more years of George, er, George, er, he - we're going to find ourselves in a position where, if Trump gets elected, we're going to be in a different world."
The concert, called I will vote, featured rapper A$AP Ferg, the Black Eyed Peas, Jon Bon Jovi and singer Cher and was livestreamed on YouTube.
As Biden spoke, his wife Jill appeared to be trying to prompt the presidential candidate with some spectators suggesting she was muttering "Trump" under her breath as her husband fumbled his words.
Biden may have been confusing Trump with President George W Bush, who held office during the Democrat's run for office with Barack Obama in 2008.
Trump was quick to seize on the gaffe, tweeting: "Joe Biden called me George yesterday. Couldn't remember my name. Got some help from the anchor to get him through the interview. The Fake News Cartel is working overtime to cover it up!"
The President's re-election campaign has repeatedly questioned Biden's fitness to govern, suggesting the 77-year-old's frequent verbal slip-ups are proof he is in cognitive decline.
Biden, who turns 78 next month, would be the oldest ever president if elected to the White House on November 3.
Earlier on Sunday, Biden was forced to defend his physical and mental competence for the top job during a CBS 60 Minutes interview.
"All I can say to the American people is: watch me, see what I've done, see what I'm going to do. Look at me. Compare our physical and mental acuity. I'm happy to have that comparison," he told interviewer Norah O'Donnell.
Trump also sat down with 60 Minutes, but walked out of the interview after claiming he was receiving a tougher grilling from the programme than Biden.
"I see Joe Biden, giving softball after softball. I've seen all of his interviews. He's never been asked a question that's hard," Trump said.
Shortly afterwards, the irate President said: "I think we have enough of an interview here... Let's go."