Biden refuses to drop out despite Democrats' doubts

US President Joe Biden refused to abandon his reelection campaign on Monday as he sought to stave off a possible revolt by 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 program. He repeated that message to donors on a private call later in the day, according to a source on the call.

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 now that lawmakers have returned to Washington after a break.

Biden faces a critical week as he tries to shore up a campaign that has been on defence 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. Other lawmakers said they supported his candidacy.

Read also: Biden seeks boost in Pennsylvania amid mounting calls to step aside

"President Joe Biden is the nominee and has been selected by millions of voters across this country," Representative Steven Horsford, chair of the Congressional Black Caucus, said on social media. Black voters are a critical part of Democrats' base of support.

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.

He will have little time to campaign this week as he hosts a meeting of NATO member states, capped with a rare solo press conference on Thursday.

The age factor

A Reuters/Ipsos poll last week found that one in three registered Democratic voters believed that Biden should quit the race, with 59% of respondents in the president's party saying he is too old to work in government.

However, that poll also found that none of his possible replacements fared better in a matchup against Trump. The poll found Biden and Trump tied at 40% each.

Biden's troubles appear to be increasing the number of races Democrats need to worry about in November.

Internal party polling shows that New Mexico and Virginia became more competitive following the debate, according to a source familiar with the findings, and the nonpartisan Center for Politics at the University of Virginia last week shifted its ratings on the states of Michigan and Minnesota to make each slightly more favourable for Republicans.

Together, those states will host a half-dozen of the most competitive House races.