The US Constitution has a built-in mechanism that allows the president’s powers to be transferred to their vice president if they become incapable of discharging them.
Both Ronald Reagan and George W Bush used the 25th Amendment to do so temporarily before they were put under medical anaesthesia.
But could it be used to oust Donald Trump if he is deemed unfit to serve? In the wake of the US Capitol riots, Democratic lawmakers have called on Mike Pence to invoke the amendment and remove Mr Trump from power. House Speaker Nancy Pelosi said she would give Mr Pence 24 hours to use the amendment to remove Mr Trump before the House moves to impeach him for a second time.
On Monday, the motion to give Mr Pence the 24 hour time slot was introduced by House Democrats, but was blocked by Republicans.
House Democrats vowed to pass the measure on Tuesday, and threatened that if by Wednesday Mr Trump is still in office, they will move on to a second impeachment.
A deployment of the 25th Amendment to oust Mr Trump would require a number of variables to fall into place: Mr Pence and eight of the 15 members of the cabinet would have to decide to go ahead with it and be prepared to prove their case before securing a two-thirds majority vote in Congress if Mr Trump were to challenge them.
But Dr Jacob Parakilas, assistant head of the US and Americas Programme at Chatham House, said he believed such a measure was “extremely unlikely”.
“The idea of it being used to forcibly depose a president is, I think, incredibly far-fetched. It would instantly create a political crisis that would very quickly become a constitutional crisis,” he said.
“You would see the emergence of factionalism within the government. It’s an incredibly powerful tool but it has the potential for spectacular levels of blowback.”
The operative part of the 25th Amendment is Section 4:
“Whenever the vice president and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide, transmit to the president pro tempore of the Senate and the speaker of the House of Representatives their written declaration that the president is unable to discharge the powers and duties of his office, the vice president shall immediately assume the powers and duties of the office as acting president.”
Experts have already said impeachment is unlikely to be a threat for Mr Trump, because of the strong position in which he has put the Republican Party.
Assistant professor Rebecca Thorpe, a political scientist at the University of Washington in Seattle, previously told The Independent: “Given Trump’s numerous financial conflicts of interests, the potential for corruption and the likely violations of the Emoluments Clause, the legal possibility for impeachment is rife.
“Trump is an unconventional Republican in many ways, but he has appointed a cabinet full [of] far-right conservatives with a conventional conservative agenda of tax cuts, reduced spending on health care and social services, and extensive deregulation.
“Thus far, he has also received support from congressional Republicans who have blocked legislation to investigate or curb Trump’s massive financial conflicts of interests.”
“Whether it will be about the Russia dossier or other scandals that are undoubtedly there, he has become a liability for the Republican Party. At some point they will need to distance themselves from him in order to solidify re-election for the House.”