Joe Biden facing revolt from within his own party as furious Democrats issue ultimatum

Joe Biden is facing a growing revolt from within his own party as donors handing him a stark ultimatum following his widely criticised debate performance last week.

Speaking to MailOnline, major Democratic donor and former hedge fund manager Whitney Tilson said: "For Biden's own good and the good of the country, he should step aside immediately."

Tilson, who has donated more than $300,000 to the party in recent years, added: "The fact that it has now been three days and Biden has done nothing to reassure us confirms my worst fears," he added.

Biden sparked concern from supporters as he struggled on the debate stage against Donald Trump on Thursday, in their first Presidential debate.

The 81-year-old appeared at times to lose his train of thought, prompting the Republican to claim at one point he couldn't understand what Biden was saying.

Biden gave a much punchier performance at a rally in North Carolina the following day, acknowledging that he couldn't debate as well as he used to, but insisting he will fight on and beat Trump.

It appeared to do little to allay fears among voters, with a CBS News/YouGov poll released on Sunday indicating that 72 percent of registered voters believe he does not have the mental and cognitive health to serve another term - a marked increase from the 65 percent answered the same way in an earlier poll.

Forty-nine percent of respondents said the same of Trump.

Despite the defiant messaging from the Biden camp in the days following the debate, his benefactors remain deeply concerned about the Democrats chances with him in the hotseat.

Biden appeared at a New York fundraiser on Sunday and, according to one attendee read a 15-minute from a teleprompter then left without taking any questions.

"Doing that for the next five months is not going to be enough," the fundraiser guest told the outlet, stressing that the President's supporters deserve reassurance that he is able to overcome Trump in November.

But a call from Democratic National Committee Chairman Jaime Harrison and Biden campaign manager Julie Chavez Rodriguez to anxious DNC members later on Saturday only served to deepen concerns.

John Verdejo, a party member from North Carolina, told thet outlet the call was "akin to a rah-rah speech," and said he was surprised the organisers didn't address the "elephant in the room" - Biden's rambling performance in Atlanta.

However, other DNC members said they felt "gaslighted" by on the call by campaign officials, who seemed to deny that the President's performance was a cause for concern.

Tilson has called for Biden to dispense with the crib sheets, teleprompters and vetted questions, and demonstrate his fitness with weekly press conferences, or by meeting with the New York Times editorial board and pursuade them they were wrong to call for him to drop out of the race.

"There is a significant amount of anxiety among Biden's advisers that one more senior moment could ratchet up the already significant pressure amongst Democrats for the president to drop out," former Obama adviser Brett Bruen told The Mail.

But despite the heat coming from Biden's backers, seeking to replace him would present a number of practical challenges.

On Saturday, Chavez Rodriguez said if Biden were to bow out only Vice President Kamala Harris would be able to spend the vast campaign warchest the president has amassed.

Federal Election Commision rules stipulate the $91.2 million the Biden-Harris ticket has collected as of May 31 can't be transferred to any other candidate, meaning Biden sceptics may not have the leverage to try and oust him.

Polls have suggested Harris herself is one of the most unpopular VPs in history, and other candidates would likely question her chances against Trump if Biden were to make way.