As a practical matter, the notion that Mr. Trump would be removed through the 25th Amendment is more opposition fantasy than plausible outcome, absent a significant change in circumstances. The amendment does not define “unable to discharge” and was devised mainly for a situation when a president had a serious health problem, not for a president whose behavior seems erratic and would fight removal.
The amendment can be put to use only if the vice president agrees, and few can imagine Mr. Pence, who has made public loyalty to Mr. Trump his calling card, going along without a more extreme situation. The amendment then requires the support of a majority of the cabinet or some other body designated by Congress. Congress has never designated such a body, leaving the matter to the cabinet.
Even if the vice president and a majority of the cabinet were to decide to invoke the amendment, there is an appeals process. The deposed president could inform Congress that he is, in fact, capable of carrying out the duties, and it would require a two-thirds vote of both the House and the Senate to reject that determination and remove him — a burden even higher than impeachment, which requires only a majority in the House as well as a two-thirds vote of the Senate for conviction and removal.