“I don’t think anybody’s more qualified to be president or win this race than me,” Mr Biden said.
President Joe Biden’s Friday night TV interview does not seem to have quelled an uprising within his own party to end his re-election campaign after a halting debate performance against Donald Trump.
A fifth House Democrat, Angie Craig of Minnesota, on Saturday joined colleagues in calling for the president to step aside, and reports suggest more could follow.
In his rare prime-time ABC News interview, Mr Biden dismissed his debate performance as just a “bad episode” and said only the “Lord Almighty” could convince him to end his bid for re-election.
Mr Biden, 81, is spending Saturday at his family home in Delaware before two public events on Sunday.
There is growing unease among Democrats, although no senior members of the party have called for him to quit.
Some polls show Trump’s lead over Mr Biden widening, and many are concerned about losing the presidency and House seats, along with the Senate majority, if he leads the ticket.
Ms Craig, who is running in a competitive district in Minnesota, said on Saturday that she did not believe Mr Biden could “effectively campaign and win against Donald Trump”.
She said that while she respected his decades of service, “there is simply too much at stake to risk a second Donald Trump presidency”.
Minutes after the ABC interview, Texas congressman Lloyd Doggett, the first House Democrat to call for Mr Biden to drop out, said on CNN that the need “is more urgent tonight than when I first called for it”.
He said the longer it took Mr Biden to make a decision to withdraw, the “more difficult for a new person to come on board who can defeat Donald Trump”.
Other House Democrats including congressman Mike Quigley of Illinois and Seth Moulton of Massachusetts called on Mr Biden to withdraw on Friday.
They join Arizona’s Raúl Grijalva’s call on Wednesday.
In his interview, Mr Biden declined to take a cognitive test and make the results public to prove he was fit to serve another term.
“I have a cognitive test every single day. Every day I have that test – everything I do [is a test],” he told George Stephanopoulos.
This response did not resonate with Democratic congresswoman Judy Chu of California, who told Politico that his answer was “unsettling and not particularly convincing” and that she would “be watching closely… especially in spontaneous situations”.
During the 22-minute ABC interview, Mr Biden rejected suggestions allies may ask him to stand aside, saying “it’s not going to happen”.
Mr Stephanopoulos pressed the president on his capacity to serve another term.
“I don’t think anybody’s more qualified to be president or win this race than me,” Mr Biden said.
Mr Biden, who is due to speak at a rally in Pennsylvania on Sunday, thanked Vice-President Kamala Harris for her support during the ABC News interview.
Ms Harris has emerged as a top contender to replace him if he were to step down.
In an interview on Saturday at the Essence black culture festival in New Orleans, the vice-president said that November’s election was crucial to American democracy, but made no mention of Democratic disquiet about Mr Biden.
“Understand what we all know – in 122 days, we each have the power to decide what kind of country we want to live in,” she said.
She said Trump “has openly talked about his admiration of dictators and his intention to be a dictator”.
Essence was the first of a number events in July that appear to target female black voters, a key constituency for Democrats in November.
However, questions around Mr Biden’s candidacy and the potential for Ms Harris to take his place will be difficult to avoid.
Ms Harris has spent the last week close to the president, flying from Los Angeles to attend the White House 4 July celebration, sitting in a meeting with governors and Mr Biden, and also being involved in his call with Benjamin Netanyahu, Israel’s prime minister.
Vice-presidents have the delicate balancing act of projecting unequivocal support for their bosses while also tacitly proving they are up to the main job. That has been more so for Ms Harris as questions swirl around Mr Biden’s re-election bid.
However, some Democrats acknowledge concerns about Ms Harris as a presidential candidate. She struggled to gain her footing early in her vice-presidency as she was given responsibility for issues including immigration, student debt and voting rights.
Low approval ratings have dogged her in office, although they have improved in recent months. She has since refocused her attention on issues such as abortion rights, which Democrats believe will be crucial in November.
BBC