Political centrist Joe Manchin is calling for Biden to drop out

Senator Joe Manchin, formerly a Democrat and now an independent, says it's time for Biden to pass the torch

Senator Joe Manchin of West Virginia is calling for Joe Biden to drop out of the 2024 race, as the fight over whether the president should stay in spreads beyond the rank-and-file of the Democratic party.

Mr Manchin is a former Democrat who became an independent in May, after he consistently sided with Republicans on issues and occasionally gave support to former President Donald Trump, a Republican.

When the nonpartisan group No Labels was considering nominating a candidate in the presidential election earlier this year, it turned to Mr Manchin, who is seen across the country as a firm centrist.

On Sunday, he said it was time for Mr Biden to "pass the torch".

“He will go down with a legacy, unlike many people, as one of finest and truly a patriot American. So with that, I come with a heavy heart to think the time has come for him to pass the torch to a new generation," Mr Manchin told ABC News.

Mr Manchin also advocated for an "open process" in the coming weeks to find a replacement.

"I think we have a lot of talent on the bench," he said.

While dozens of House Democrats have called for Mr Biden to step down, worried he has a losing campaign that will hurt their chances in November, only a handful of senators have done so. At least two of the four who have pressed him to quit the race - Ohio's Sherrod Brown and Montana's Jon Tester - are stalwart Democrats facing tough re-election battles.

Mr Manchin, though, does not face those stakes.

Neither does Colorado Gov. Jared Polis, a moderate Democrat whose term does not expire until 2027, and who is currently head of the bipartisan National Governors Association.

The governor did not directly call for Mr Biden to step aside, but told CNN that polling numbers show "we need to change something about what we're doing."

"The burden is on him to really show 'Hey, I'm the guy with the plan for the next four years. I can turn it around, and you don't need to hold your breath every time I talk, because we got this,'" he said. "And he hasn't done that yet."

Big-ticket donors have warned that the money will dry up and former House Speaker Nancy Pelosi, one of the strongest forces in the Democratic party, have consistently pushed Mr Biden to drop out as he still struggles to rebuild voter confidence nearly a month after his disastrous debate performance.

The president, who expects to return to the campaign trail this week, has said the majority of his party is behind him and that he believes he can beat his rival Donald Trump. Mr Biden had to press pause on campaigning in recent days to recover from Covid-19.

Former President Bill Clinton and his wife, the 2016 Democratic nominee, Hillary Clinton are reportedly asking donors to stick with Mr Biden, according to US media.

Recent polls, meanwhile, show him trailing Trump by a few points in several key swing states.

Trump's lead over Mr Biden has grown since a 20-year-old gunman attempted to assassinate him last week at a rally in Pennsylvania. The former president appeared at his first rally since the attack on Saturday before a crowd of thousands in Grand Rapids, Michigan.

Top Democrats in the House on Sunday took to the Washington talk shows to make clear they support Biden staying in the race.

South Carolina's Jim Clyburn, a longstanding leader in the House and among black lawmakers, told CNN that the Democratic Party should "coalesce" around Mr Biden.

He said he would only support Mr Biden stepping down if the president made the choice himself, adding Democrats needed to "honour" the nominating process.

Republican House Speaker Mike Johnson, meanwhile, said there could be legal action against Democrats if they chose to change their nominee.

"It will be very interesting to see if the so-called party of democracy, the Democrats, go into a backroom somewhere and switch it out and put someone else at the top of the ticket," he said. "They've got legal hurdles in some of these states, and it'll be litigated."

It is possible for Mr Biden could exit the race and release all of his pledged delegates to vote for a candidate of their choosing, leading to an open convention.

The Democratic National Convention begins 19 August, but the party is expected to meet virtually before then to nominate Biden as its official nominee.

The DNC rules committee met last week to discuss the procedures for the virtual roll-call vote, during which the committee's co-chair Leah Daughtry said that "any challenger would have to have the verified support of hundreds of delegates".

The committee is also meeting on Sunday to discuss roll-call voting rules, a new process for the party that could be cancelled in light of the party infighting over his nomination.