Final answer:
If a president contests a previous assertion of incapacity, the vice president and the executive department heads have four days to reaffirm the president's disability. Congress then has 48 hours to gather (if not in session) and a 21-day period to determine, by a two-thirds majority, whether the president is disabled, during which the vice president serves as acting president.
Step-by-step explanation:
Procedure When a President's Disability is Disputed
If a president disputes a previous declaration of disability, the process to resolve whether the president is incapacitated depends on several time-sensitive steps. Initially, there is a four-day period for the vice president and a majority of the principal officers of the executive departments to reassert the president's disability to the Speaker of the House and the President pro tempore of the Senate. Should a second declaration be made, Congress, if not already in session, must convene within 48 hours to address the situation.
An important timeline begins once the vice president's second declaration of disability is submitted. Congress then has 21 days to make a decision on the president's ability to discharge the powers and duties of their office. A two-thirds majority in both the House and the Senate is necessary to confirm the president's disability. During this period, the vice president assumes the role of acting president. If Congress supports the declaration of disability, then the vice president continues in this capacity. Conversely, if Congress cannot reach the required majority within the 21-day limit, the president is entitled to resume their responsibilities.