If the Democrats wish to now introduce a new candidate to run against Mr Biden for the nomination they would be severely inhibited as 80 per cent of the upcoming primary contests have closed applications for new entries.
Any rule changes to allow for a new candidate on the ballot in those states would have to be passed by the party’s Biden-backing Rules and Bylaws Committee.
In theory, delegates who have already pledged their support for Mr Biden but are now concerned by his mental state could defect when it came to a floor vote. But that is considered highly unlikely.
“There is no mechanism that could force him out. That could only happen voluntarily,” explained Christopher Galdieri, professor of politics at Saint Anselm College in New Hampshire.
“If he were to stand aside a lot would depend on timing. If it took place after the primaries, when all the delegates had been selected they would make the decision at the convention.
“You would have a throwback to the 19th century where the nomination was fought out on the floor, rather than rubber-stamping the primary and caucus results.”
Professor Galdieri said if Mr Biden dropped out while the primaries were in full flow “There would be absolute chaos. Biden’s name would be on most of the ballots.
“In other states, there would be a scramble,” he added.
“Either way it would be the worst of both worlds, There would be very short notice.
“Candidates who have not been through the wringer would turn up at the convention and tear each other apart.”