In a particularly significant blow to President Joe Biden, prominent Democrat Adam Schiff – a California congressman running to be the state’s next senator – has called on him to “pass the torch” and allow another Democrat to challenge Donald Trump in November.

Mr Schiff’s announcement comes shortly after the Democratic National Committee announced its plans to hold a virtual roll-call vote in early August to formally elect Mr Biden as the party’s nominee, despite calls to replace him over concerns for his cognitive health.

Presidential nominees typically receive their formal nomination at their party’s in-person convention – which begins on 19 August in Chicago for Democrats – but Mr Biden’s party has sped up the process to comply with a 7 August candidate certification deadline in the state of Ohio.

With the number of calls for Biden to step aside growing, several Democrats have demanded the party cancel the virtual vote and allow for an open convention.

It appears it is not just party insiders calling for such a change. New polling suggests nearly two-thirds of Democrats believe Mr Biden, 81, should step aside and let the party nominate somebody else.

Jaime Harrison, the chair of the Democratic National Committee, has sought to push back on the rising doubts about the nominating process. He noted on X, formerly Twitter, that the party “will have this vote by August 5th”.

The announcement was also made in a letter obtained by CBS News, the BBC’s US partner, that emphasised the Ohio candidacy deadline.

“We will not be implementing a rushed virtual voting process,” Leah Daughtry and Tim Walz, chairs of the convention rules committee, wrote, and “no voting will begin before August 1”.

But, they added, Ohio’s 7 August filing deadline could risk ballot access and ballot -related litigation. They feared any delay could “jeopardize whether the Democratic ticket appears on the ballot in must-win states”.

Some Democrats have criticised party leaders for this response, as Ohio lawmakers voted to move the state deadline to 1 September. The law, however, comes into effect on that same day, raising fears that it could lead to litigation.

Still, some Democrats warned an early vote was a “terrible idea”, as forcing one through while discussions about replacing Mr Biden continued could “deeply undermine the unity and morale of Democrats”.

Mr Biden is still working to salvage his candidacy nearly four weeks after a CNN debate against Donald Trump. The president has since admitted that he “screwed up” during the debate.

Polling of the 2024 race continues to show the two locked in a tight race, but with Mr Biden trailing his Republican rival in battleground states and leading him by surprisingly narrow margins in states usually won by Democrats, such as Virginia and Minnesota.

Mr Schiff, the prominent California Democrat, said on Wednesday that Mr Biden “has been one of the most consequential presidents in our nation’s history, and his lifetime of service as a Senator, a Vice President, and now as President has made our country better”.

But Mr Schiff said that the president could “secure his legacy of leadership” by allowing Democrats to support

“Our nation is at a crossroads. A second Trump presidency will undermine the very foundation of our democracy, and I have serious concerns about whether the President can defeat Donald Trump in November,” he added.

Frustrations also spilled over this weekend on a call between a group of moderate House Democrats and Mr Biden, according to CBS.

Participants described the president as “defensive” and “rambling” in his answers, at one point lashing out at Colorado Democrat Jason Crow when questioned about his campaign strategy.

The congressman told CBS’ Face the Nation programme this Sunday there is now a “high risk” Democrats will lose the election “unless there is a major change”.

“Reading the tea leaves is very troubling for many of us right now,” Mr Crow said. “So we want to see a change.”

But party members have largely stifled their public calls for Mr Biden to withdraw from the race since Saturday’s attempted assassination of Mr Trump.

After a brief pause following that incident, the president resumed campaigning on Tuesday and Wednesday in the battleground state of Nevada.

He was joined by some of his top defenders, including Congressman Jim Clyburn, Congressional Black Caucus Chair Steven Horsford and Congressional Hispanic Caucus Chair Nanette Barragan. Both caucuses have recently reaffirmed their support for him.

In a Monday interview with NBC News, Mr Biden said his mental acuity has been “pretty damn good”.

“I’ve gotten more done than any president has in a long, long time in three and a half years. So I’m willing to be judged on that.”