Does anyone care what Trump "demands"? Sounds like he is looking for an excuse not to debate.
I don't think the 25th amendment uses the term "mentally unfit."
The 25th Amendment DOES use the term "mentally unit."
But, generally speaking, the 25th Amendment is incapable of removing a President who is mentally unfit for office (except in cases like, for exampl, massive stroke, or severe head trauma that leaves a President CONSPICUOUSLY and severely mentally incompetent)
Otherwise, the 25th Amendment is fatally- flawed instrument. Firstly because even if a certain President is suspected of being mentally unfit to discharge the duties and responsibilities of his office, the decision to invoke the 25th, and ultimately decide whether a President must stand down (if he judged to be, say, "mentally unfit" is not made by an authorised panel/s independent, medical experts; rather, the whole process it is placed in the hands politicians, in particular the Vice President, the Heads of Department in the Executive Branch (i.e. the members of Cabinet) and ultimately the members of Congress . The two relevant sections of the 25th Amendment here are Section (3) and Section (4).
SECTION (3)
Provides that if the President on his own sends a "written declaration" to the Senate and the House that " he is unable to discharge the powers and duties of his office," the Vice President remains the "acting President" until the President sends notice to the Senate and the House that he can once again assume his role as President.
Even if we both assume there is a substantive medical issue with Biden (on a personal note I am, absolutely certain that he has all the classic cognitive symptoms of advanced Vascular Dementia; I also believe that Biden has, in fact, he has been made aware of this through discrete, medical advice>. In any case, do you think Biden has the slightest intention of voluntarily ceding control to a nit-wit - and a very unpopular nit-wit at that - KAMALA HARRIS.
I DON'T THINK SO FLASH. WHAT ABOUT YOU ?
SECTION (4)
Section (4) is the provision of the 25th Amendment that applies to a President who is suffering from a mental disability, BUT WHO IS UNWILLING OR UNABLE TO GIVE UP CONTROL OF THE EXECUTIVE BRANCH. Section (4) provides that when the
"Vice President and a majority of either the Principal Officers of the Executive Departments or other such body as Congress may by law provide'" they may send written notice to the Senate and the House that the President is "unable" to do his job, and the Vice President becomes acting President.
The President can reclaim the duties of his office if he sends written notice that he is capable of being President unless the the group that removed him disagrees within 4 days. If this conflict arises, CONGRESS MUST ASSEMBLE WITHIN 48 HOURS AND HAS 21 DAYS TO DECIDE WHO IS RIGHT.
IT TAKES A TWO THIRDS VOTE OF BOTH HOUSES OF CONGRESS TO OVERRIDE THE PRESIDENT'S ASSERTION THAT HE CAN RESUME HIS OFFICE.
In Frebruary of this year Donald Trump and a number of other prominent Republican politicians called from the 25 Amendment (Section 4) to be invoked in respect of Biden's being mentally unfit to discharge his duties as President. But surely they knew that this was a futile gesture. I mean it is, of course, EXCEEDINGLY UNLIKELY for multitudinous, political reasons that Kamala Harris and a majority of Biden's Cabinet would send Congress that notification. Don't you agree, FLASH.
(1) THE 25th AMENDMENT IS A TOTALLY FLAWED INSTRUMENT. ONE RESAON IS THAT IT ASSUMES POLITICIANS HAVE EXPERT MEDICAL KNOWLEGE (WHICH THEY DO NOT WITH THE RARE EXCEPTION OF CONGRESSMEN LIKE PAUL RAND).
(2) IN THE CASE WHERE A PRESIDENT (like BIDEN) IS, IN FACT, MENTALLY UNFIT FOR OFFICE< PARTISAN POLITICAL MANOEUVRING WILL ENSURE THAT NOTHING IS/CAN EVER DONE TO REMOVE HIM.
(3) I HAVE A BRILLIANT PLAN FOR REWRITING THE MOST IMPORTANT
I HAVE WRITTEN A BRILLIANT (EVEN IF I DO SAY SO MAYSELF 
)RE-DRAFT OF THE 25th AMENDMENT, FLASH, THAT IRONS OUT THESE PROBLEMS. YOU ARE WELCOME TO A PRECIS OF IT IF YOU LIKE !!
Dachshund - the WONDER HOUND
DLM....Dachshund Lives Matter !!
