United States legislator Adam Schiff, an influential member of Joe Biden’s Democratic Party, has joined a chorus of calls urging the US president to drop out of the 2024 election race.

In a statement shared by US media outlets on Wednesday, Schiff said he has “serious concerns” about Biden’s ability to beat his predecessor and Republican presidential nominee Donald Trump at the ballot box in November.

“While the choice to withdraw from the campaign is President Biden’s alone, I believe it is time for him to pass the torch,” said Schiff, a US congressman who is expected to win an open Senate seat in California in the upcoming election.

“And in doing so, secure his legacy of leadership by allowing us to defeat Donald Trump in the upcoming election.”

Schiff is the latest Democratic member of Congress to call on Biden to end his re-election bid after a disastrous debate performance late last month raised concerns about his age and ability to serve another term in the White House.

The US president, 81, has resisted calls to step aside in favour of Vice President Kamala Harris or another possible replacement, insisting that he has more work to do.

“I’ve got to finish this job because there’s so much at stake,” Biden told reporters last week at the end of a NATO summit in Washington, DC.

In an address on Tuesday at the national convention of the NAACP, the largest Black civil rights organisation in the country, Biden also hit out at his Republican rival’s policies.

The Democrat had promised to promote unity after a failed assassination attempt against Trump at a campaign rally on Saturday, but told the crowd that “just because our politics are very divided doesn’t mean we should stop telling the truth”.

“Who you are, what you’ve done, what you will do — that’s fair game,” he said.

Polling in the aftermath of the Pennsylvania rally shooting has shown Trump and Biden still locked in close races in several US swing states, which will be key in determining who wins the White House.

But a poll released by the AP-NORC Center for Public Affairs Research on Wednesday showed that nearly two-thirds of Democrats believed Biden should drop out of the race and allow the party to choose a new candidate.

Only about three in 10 Democrats also said they were extremely or very confident that Biden has the mental capability to serve effectively as president, down slightly from 40 percent that said the same in a February poll.

Still, The Associated Press news agency and other US media outlets have reported that Democrats are looking to hold a virtual vote to formally make Biden the nominee in the first week of August.

That’s ahead of the Democratic National Convention, which is being held in Chicago from August 19 to 22 and is typically where the party’s presidential nominee would be confirmed.

The party announced in May that it would move forward with what’s known as a “roll call” to ensure Biden would meet a deadline to qualify for the ballot in Ohio. The US state originally had an August 7 deadline, but it has since changed its rules.

The Biden campaign has insisted, however, that Democrats must operate under Ohio’s initial rules to ensure Republican lawmakers can’t mount legal challenges to keep the president off the ballot.

The Democratic National Convention’s rules committee will meet on Friday to discuss its plans for the early roll call, according to a letter sent to members and obtained by AP, and will finalise them next week.

The letter from co-chairs Bishop Leah D Daughtry and Minnesota Governor Tim Walz states that the virtual vote won’t take place before August 1, but that the party is still committed to holding one before August 7.

“We will not be implementing a rushed virtual voting process,” Daughtry and Walz wrote, “though we will begin our important consideration of how a virtual voting process would work.”

But a contingent of House Democrats wary of swiftly nominating Biden as the party’s pick for re-election have circulated another letter raising “serious concerns” about plans for a virtual roll call.

Their letter to the Democratic National Committee, which has not yet been sent, says it would be a “terrible idea” to stifle debate about the party’s nominee with the early roll call vote.

“It could deeply undermine the morale and unity of Democrats,” said the letter, also obtained by AP.