President Joe Biden has blamed his poor debate performance last week on jet lag, telling reporters that he “wasn’t very smart” for “travelling around the world a couple of times” before the debate.
“I didn’t listen to my staff… and then I nearly fell asleep on stage,” he said.
Mr Biden, 81, last returned from travel on 15 June, nearly two weeks ahead of the 27 June debate.
The president’s remarks come amid intra-party panic ahead of November’s election over his mental fitness, and after a congressman from Texas became the first sitting Democratic lawmaker to call for him to step aside following the debate.
“I am hopeful that he will make the painful and difficult decision to withdraw,” Rep Lloyd Doggett said in a statement on Tuesday.
Mr Biden appeared to struggle through some responses during a debate with former President Donald Trump last Thursday.
“It’s not an excuse but an explanation,” he said at a private fundraiser in Virginia on Tuesday evening, referring to his travel.
He also apologised for his performance and said it was “critical” that he win re-election, according to ABC News.
Mr Biden made two separate trips to Europe within two weeks last month.
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