United States President Joe Biden has pledged to continue his re-election campaign “to the end”, as the embattled Democrat fights to keep his candidacy alive amid growing alarm over his physical and mental fitness.

Biden, 81, on Wednesday insisted that he would keep running despite growing pressure from within his party to step aside following last week’s disastrous debate performance against his Republican challenger Donald Trump.

“Let me say this as clearly as I possibly can, as simply and straightforward as I can: I am running … no one’s pushing me out,” Biden said on a call with campaign staffers.

“I’m not leaving. I’m in this race to the end, and we’re going to win.”

Biden’s defiant remarks came after US media reports indicated that the president and his team have acknowledged that his candidacy is at risk of collapsing within days if he cannot convince the public of his fitness for office.

White House spokeswoman Karine Jean-Pierre denied those reports, insisting Biden was “clear-eyed, and he is staying in the race”.

Concerns about Biden’s age and condition have boiled over since last Thursday’s debate, when the president gave several answers that meandered into incoherence.

While acknowledging that Biden performed poorly at the debate, his team has dismissed suggestions that he has dementia or is otherwise cognitively impaired.

White House officials initially blamed Biden’s poor performance on a cold.

Biden on Tuesday said he had been exhausted after making back-to-back trips to France and Italy, although he spent the week leading up to the debate behind closed doors at the presidential retreat, Camp David.

Raul Grijalva, a House representative from Arizona, on Wednesday became the second elected Democrat to call on Biden to step aside, following Texas Congressman Lloyd Doggett the previous day.

Several other elected Democrats have publicly questioned Biden’s condition or said they believe he will lose against Trump in November.

“The unfortunate reality is that the status quo will likely deliver us President Trump. When your current strategy isn’t working, it’s rarely the right decision to double down,” Seth Moulton, a Democratic representative from Massachusetts, said in a statement on Wednesday, adding that he was “taking time” to consider the best path forward for his party. (AlJazeera)