U.S. President Joe Biden has admitted his subpar performance in the recent presidential debate against Republican rival Donald Trump, attributing it to jet lag from two international trips in June. The 81-year-old president faced severe criticism for his shaky and stumbling debate delivery, with a Democratic member of the House of Representatives openly calling for him to withdraw from the presidential race.During the debate, Biden, sounding hoarse, delivered a halting performance, stumbling over his words multiple times. Some Democrats privately expressed concerns that his performance could be a disqualifying factor. Trump, meanwhile, repeated several debunked claims, including that migrants have caused a crime wave, Democrats support infanticide, and that he won the 2020 election.Jet Lag and ApologiesI didnt have my best night, but the fact is that, you know, I wasnt very smart. I decided to travel around the world a couple times, going through around 100 time zones ... before ... the debate. I didnt listen to my staff and came back and nearly fell asleep on stage, Biden said at a campaign event in McLean, Virginia, on Tuesday evening. He apologised for his performance, stating, Its not an excuse but an explanation.Last month, Biden travelled to France and Italy on two separate trips within two weeks, flying overnight from the G7 summit in Italy to attend a fundraiser with former President Barack Obama in Los Angeles on June 15 before returning to Washington the following day.Calls for ReplacementThe New York Times editorial board, which endorsed Biden in 2020, urged him to step aside to give the Democratic Party a better chance of defeating Trump with a different candidate. The greatest public service Mr. Biden can now perform is to announce that he will not continue to run for re-election, the editorial stated.White House officials attributed Bidens halting debate performance to a cold, although Biden did not mention being ill during Tuesdays fundraiser. A Reuters/Ipsos poll revealed that one in three Democrats think Biden should end his reelection bid following the debate, though no prominent elected Democrat outperforms Biden in a hypothetical matchup against Trump.U.S. Representative Lloyd Doggett became the first congressional Democrat to call for Biden to withdraw from the race, praising Bidens transformational first term but stating it was time for another party member to challenge Trump. Bidens team has been working to reassure key donors that he remains the best choice against Trump.Democratic Leaders Stand by BidenDemocratic leaders have, for now, dismissed the idea of replacing Biden. Absolutely not, said Georgia Democratic Senator Raphael Warnock, a potential replacement candidate. Bad debates happen, he told NBCs Meet the Press. The question is, Who has Donald Trump ever shown up for other than himself and people like himself Im with Joe Biden, and its our assignment to make sure that he gets over the finish line come November.