"I know I'm not a young man, to state the obvious," an ebullient Biden said at a rally one day after the head-to-head showdown with his Republican rival, which was widely viewed as a defeat for the 81-year-old president.
"I don't walk as easy as I used to, I don't speak as smoothly as I used to, I don't debate as well as I used to," he said, as the crowd chanted "four more years."
"I would not be running again if I didn't believe with all my heart and soul that I could do this job. The stakes are too high," Biden said.
Biden's verbal stumbles and occasionally meandering responses in the debate heightened voter concerns that he might not be fit to serve another four-year term and prompted some of his fellow Democrats to wonder whether they could replace him as their candidate for the November 5 US election.
Campaign spokesperson Michael Tyler said there were no conversations taking place about that possibility. "We'd rather have one bad night than a candidate with a bad vision for where he wants to take the country," he told reporters aboard Air Force One.
The campaign held an "all hands on deck" meeting on Friday afternoon (local time) to reassure staffers that Biden was not dropping out of the race, according to two people familiar with the meeting.
Though Trump, 78, put forward a series of falsehoods throughout the debate, the focus afterward was squarely on Biden, especially among Democrats.
Hakeem Jeffries, the Democratic Party leader in the US House of Representatives, avoided answering directly when asked whether he still had faith in Biden's candidacy.
“I support the ticket. I support the Senate Democratic majority. We're going to do everything possible to take back the House in November. Thank you, everyone,” he told reporters.
Some other Democrats likewise demurred when asked if Biden should stay in the race. "That's the president's decision," Democratic Senator Jack Reed told a local TV station in Rhode Island.
But several of the party's most senior figures, including former House Speaker Nancy Pelosi and California Governor Gavin Newsom, said they were sticking with Biden.
"Bad debate nights happen. Trust me, I know. But this election is still a choice between someone who has fought for ordinary folks his entire life and somebody who only cares about himself," former Democratic president Barack Obama wrote on X.
The Biden campaign said it raised $US14 million ($NZ23m) on Thursday and Friday and posted its single best hour of fundraising immediately after the Thursday night debate. The Trump campaign said it raised $US8 million on the night of the debate.
One possible bright spot for Biden: preliminary viewership data showed that only 48 million Americans watched the debate, far short of the 73 million who watched the candidates' last face-off in 2020.
Biden, already the oldest American president in history, faced only token opposition during the party's months-long nominating contest, and he has secured enough support to guarantee his spot as the Democratic nominee.
Trump likewise overcame his intra-party challengers early in the year, setting the stage for a long and bitter general election fight.
If Biden were to step aside, the party would have less than two months to pick another nominee at its national convention, which starts on August 19 - a potentially messy process that could pit Kamala Harris, the nation's first Black female vice president, against governors and other officeholders whose names have been floated as possible replacements.
TRUMP TARGETS VIRGINIA
At an afternoon rally in Chesapeake, Virginia, Trump told supporters that he had a "big victory against a man looking to destroy our country."
"Joe Biden's problem is not his age," Trump said. "It's his competence."
Trump advisers said they thought the debate would bolster their chances in Democratic-leaning states like Virginia, which has not backed a Republican presidential candidate since 2004.
Beforehand, some Trump supporters said they were struck by Biden's poor performance. “I’m scared they are going to replace him and put up somebody more competitive,” said Mike Boatman, who said he had attended more than 90 Trump rallies.
Trump fundraisers said they were fielding enthusiastic calls from donors. "Anyone who raises money knows there's a time to go to donors, and this is one of those watershed moments," said Ed McMullen, who served as ambassador to Switzerland during Trump's presidency.
Questions about Trump's fitness for office have also arisen over his conviction last month in New York for covering up a hush money payment to a porn star, his efforts to overturn the 2020 election and his chaotic term in office.
He is scheduled to be sentenced on July 11, just days before his party convenes to formally nominate him. He still faces three other criminal indictments, though none appears likely to reach trial before November.
Biden's shaky performance in the debate drew stunned global reactions on Friday, prompting public calls for him to step aside and likely leaving some of America's closest allies steeling for Trump's return.
