Final answer:
The Vice President assumes the duties of the President if the President is unable to perform them. If both are unable to serve, Congress determines the next officer to act as President. The 25th Amendment of the U.S. Constitution outlines this process.
Step-by-step explanation:
Presidential Succession
In the event that a President is unable to perform the duties of the office, the U.S. Constitution provides clear guidelines on who should assume these duties. According to the 25th Amendment of the Constitution, if the President is removed from office, dies, resigns, or is unable to discharge the powers and duties of the presidency, the Vice President shall take over as Acting President. Moreover, if both the President and Vice President are unable to serve, Congress has the authority to declare by law which officer shall then act as President.
Section 4 of the 25th Amendment further elaborates on the process. If the Vice President and a majority of the principal officers of the executive departments, or another body that Congress may designate, submit a written declaration to the President pro tempore of the Senate and the Speaker of the House that the President is unable to perform their duties, the Vice President immediately assumes the role of Acting President. If the President disputes this claim, Congress must assemble and determine the outcome. A two-thirds vote in both houses is required to confirm the President's inability, and if confirmed, the Vice President continues to act as President.