WASHINGTON: President Joe Biden said on Monday that he would not abandon his reelection campaign as he sought to stave off a possible revolt from fellow Democrats who worry the party could lose the White House and Congress in the Nov 5 US election.

Biden, 81, said any candidates who doubt his ability should challenge him at the Democratic National Convention in August - an effort that stands no chance of success unless he lets the delegates he won in primaries this year consider other candidates.

"The bottom line here is that I am not going anywhere," Biden said in a phone call he placed to MSNBC's Morning Joe programme.

Separately he told wavering Democratic lawmakers in a letter that they needed to close ranks behind his candidacy.

Several have called for him to drop out, and more could do so in coming days as lawmakers return to Washington after a break.

Biden faces a critical week as he tries to shore up a campaign that has been on defense since a shaky June 27 debate against Republican Donald Trump, which raised questions about his ability to do the job for another 4-1/2 years.

Though he has secured enough delegates to win the Democratic presidential nomination, some donors and lawmakers have called for him to step aside and let Vice President Kamala Harris or another candidate lead the ticket.

Several senior House Democrats called for Biden to drop out in a Sunday phone call, media outlets reported, though other lawmakers said they supported his candidacy.

In his letter to Democrats, Biden said he was aware of their concerns but said it was time to put them aside.

On MSNBC, Biden sounded a defiant note against wealthy donors who have called for him to drop out. "I don't care what the millionaires think," he said.

A growing number of Democratic lawmakers have voiced concern that his poor public approval ratings, plus concerns about his age and ability, could hurt the party's prospects for retaining the Senate, which they control by a 51-49 majority, and winning back the House, where Republicans have a 219-213 majority.

If Republicans were to capture the White House and both houses of Congress, Trump would face few constraints on his ability to push through major policy changes.

Biden on Sunday made a series of campaign appearances in Pennsylvania, a battleground state that traditionally can decide an election.

He was joined by Senator John Fetterman, a high-profile Democrat who has rejected calls for Biden to drop out.

Biden will go on meeting voters at churches, union halls and other venues in coming days, administration officials said.

At the same time he plans to reach out to lawmakers he has known for decades, they said, as he tries to calm concerns.

  - Reuters