The Speaker of the House of Representatives, Nancy Pelosi, and the Democratic leader in the Senate, Chuck Schumer, have both called for President Trump to be removed from office and Pelosi is not the only politician to specifically talk about invoking the 25^th.

But the 25^th amendment to the US constitution - specifically section 4 of the amendment - is untested, unpredictable, complex and clumsy, and could well do more harm than good, even if it could be invoked in this instance.

Moreover, it wouldn't actually remove Trump from the presidency, but simply transfer the powers and duties of the office to the Vice-President for an uncertain period of time. Donald Trump would remain as President and would still occupy the White House. Mike Pence would only be acting President, even though he would assume all the powers and duties of the office.

When you take into account Trump's apparent unhinged state of mind, anyone invoking the 25^th amendment would need to be sure of how Trump would behave if deprived of his power against his will.

In the case of Donald Trump, the 25^th amendment is not fit for purpose. In order to protect the United States against further irrational acts he may instigate in the last 12 days of his presidency, its political leaders need to focus elsewhere.

The 25^th amendment was ratified in 1967 and establishes a process whereby a president who is "unable to discharge the duties of his office" can be temporarily relieved of his responsibilities by the vice-president assuming the role of acting president.

It is not a vehicle for permanently removing a president from office, but a mechanism for a temporary transfer of power during a period of presidential illness or incapacity.

Section 4 of the amendment works like this: the vice-president and "a majority of either the principal officers of the executive departments or such other body as Congress may by law provide" declare to the speaker of the House of Representatives and oresident pro tempore of the Senate that the president is incapacitated. Henceforth, the vice-president becomes acting president until such time as the president submits a written declaration to the contrary.

The uncertainty in the process stems from the provision that allows the president to override the determination of the vice-president and what amounts to a majority of the cabinet - Congress hasn't provided for any "such other" body to date - by simply informing Congress that "no inability exists".

Thereafter, the president resumes the powers and duties of the presidency unless the vice-president and a majority of the heads of the executive departments challenge the president's response within four days. In other words, the vice-president would have to move against the president twice.

If that happened, then the scene would move to the US Congress. The legislative body would have 21 days to debate and decide the issue by a two-thirds vote of both houses.

This means the implementation of the 25^th amendment is dependent initially on the willingness of one person - the vice-president of the United States - to support the move (because it doesn't work with just a majority of the cabinet alone) and, ultimately, on the support of a two-thirds vote in both houses of Congress. That means just 34 members of the US Senate is all it takes to block the transfer of the powers of the presidency from Donald Trump.

READ MORE:

There is an argument amongst the experts about whether the kind of disability envisaged by the framers of the 25^th amendment included mental incapacity. Uppermost in their minds was physical disability, like the massive stroke suffered by Woodrow Wilson in October 1919 that paralysed him and his presidency for the next 17 months, or the slow death of President Garfield who was assassinated in 1881, but lingered for 80 days before he died. The amendment would work reasonably well in those circumstances, with little prospect of the afflicted president invoking the "no inability exists" provision.

Section 4 of the amendment has never been invoked. And Donald Trump, whatever his mental state, is not physically disabled. Even if Vice-President Pence and the heads of the executive departments deem him to be mentally disabled - still an unlikely prospect at the moment - he would easily have the capacity to respond with a "no inability exists" letter to Congress and set in train what would become a constitutional nightmare that in all probability would disable the executive and legislative branches of government.

He would also have the capacity to use the media and rally his supporters to press his cause and disrupt American politics right up until noon on January 20 - and maybe even beyond that.

Donald Trump is not the first, nor is he likely to be the last, American president whose mental health has been or will be questioned. And, while the 25^th amendment may be a useful provision for dealing with physical disability in the White House, it is less than adequate as a mechanism for responding to mental disability in the president.

The core problem is that the mechanisms of presidential accountability in the United States constitution are too limited and too difficult to implement. Impeachment is the first, last and only constitutional method of holding a president accountable for his actions. The 25^th amendment was never intended to be an additional form of accountability, just a way of dealing with a temporary problem of presidential disability. It shouldn't be used for managing the Trump problem in the dying days of his presidency. It is just too uncertain for that.