Section 4 of the 25th Amendment provides, in relevant part, a process to declare the President unable to perform the duties of the office. If the Vice President and a majority of the Cabinet (or of another body as Congress may by law provide) submit a declaration to Congress, the Vice President immediately assumes the role of Acting President. When this declaration is transmitted to the President pro tempore of the Senate and the Speaker of the House of Representatives to Congress, the Vice President immediately assumes the role of Acting President.
This market will resolve YES when this initial declaration is transmitted regardless of subsequent action (e.g. congressional overruling, judicial intervention, refusal of the president to step aside, etc.).
The invocation of Section 3 will under no circumstances resolve this market to YES unless Section 4 is invoked after the invocation of Section 3.
Any and all Constitutional questions will be resolved in accordance with the article linked here unless the Supreme Court issues a controlling opinion that is directly contrary to an opinion expressed in the article at least 6 weeks before the invocation of Section 4.