It comes as Arizona congressman Raul Grijalva says Biden has a responsibility to “get out of this race”.

“I’m in this race to the end and we’re going to win,” Biden said on a call with staffers from his re-election campaign.

A top White House aide also posting on the X social media platform that Biden said: “I am running. I am the leader of the Democratic Party. No one is pushing me out”.

The president was pulling every possible lever to try to salvage his re-election campaign — talking to top legislators, pumping up his campaign staff and meeting later in the day with Democratic governors before a planned weekend blitz of travel and a network TV interview.

But there were mounting signs that support for Biden was rapidly eroding among Democrats on Capitol Hill.

Democrat representative Jim Clyburn, a longtime Biden friend and confidant, said he would back a “mini-primary” in the run-up to the Democratic National Convention next month if Biden were to leave the race.

Clyburn, floated an idea that appeared to be laying the groundwork for alternatives by delegates during the Democrats’ planned virtual roll call that is scheduled before the more formal party convention, which is set to begin August 19 in Chicago.

“You can actually fashion the process that’s already in place to make it a mini-primary and I would support that,” Clyburn told CNN.

He said Vice President Kamala Harris, governors and others could join the competition.

“It would be fair to everybody. … Because if she were to be the nominee we need to have a running mate. And need a strong running mate.”

Clyburn, a senior lawmaker who is a former member of his party’s House leadership team, said he has not personally seen the president act as he did on the debate stage last week.

“I saw what I saw last Thursday night, and it is concerning,” Clyburn said.

Some suggested Harris was emerging as the favourite to replace Biden if he were to withdraw, although those involved in private discussions acknowledge that govenors Gavin Newsom of California and Gretchen Whitmer of Michigan remain viable alternatives.

But for some insiders, Harris is viewed as the best prospect to quickly unify the party and avoid a messy and divisive convention fight.

Harris has been the White House’s first line of defence for Biden since the debate.

She conceded to a few dozen donors in San Francisco, the president’s performance was “not his finest hour.”

However, she said: “the outcome of this election cannot be determined by one day in June”.

Only 39 per cent of US adults have a favourable view of Harris, which is in line with Biden’s 40 per cent, according to an AP-NORC poll conducted in June.

However, her unfavourable rating is 49 per cent, lower than Biden’s 57 per cent, and 12 per cent said they weren’t familiar enough with Harris to have an opinion of her.

Even as pressure around Biden mounted, he and Harris made a surprise appearance on a call with staffers from his re-election campaign and offered a pep talk, stressing how important it was to beat Republican Donald Trump in November and returning to Biden’s previous post-debate vow that when he gets knocked down, he gets up again.

The president told those assembled that he was not leaving the race and would not be dragged out.

Harris added: “We will not back down. We will follow our president’s lead. We will fight, and we will win”.

White House press secretary Karine Jean-Pierre was asked during her briefing with reporters a short time later whether Biden would consider stepping down.

“Absolutely not,” she said.

She added that he “is clear-eyed. And he is staying in the race.”

with AP