Page "President of the United States" Paragraph 60

Under Section 4 of the Twenty-fifth Amendment, the vice president, in conjunction with a majority of the Cabinet, may transfer the presidential powers and duties from the president to the vice president by transmitting a written declaration to the Speaker of the House and the president pro tempore of the Senate that the president is unable to discharge the presidential powers and duties.

If this occurs, then the vice president will assume the presidential powers and duties as acting president ; however, the president can declare that no such inability exists and resume the discharge of the presidential powers and duties.

If the vice president and Cabinet contest this claim, it is up to Congress, which must meet within two days if not already in session, to decide the merit of the claim.