The first section of the Twenty-fifth Amendment codified the traditionally observed process of succession in the event of the death of the president of the United States, which is that the vice president would succeed to the office. It also specifies that, should the president resign, the vice president would assume the title and position of president.
The second section says that, in the event of a vacancy in the office of the vice president, the president is to nominate a vice president, who would be subject to confirmation by the U.S. Congress.
The third section sets forth the formal process for determining the capacity of the president to “discharge the powers and duties of his office,” as the amendment reads. It assumes that the president is capable of producing a written statement formally notifying the president pro tempore of the Senate and the speaker of the House of such circumstances, which would result in the vice president’s temporarily serving as acting president.
In the event that a president may be unable to declare his inability to discharge the powers and duties of office, the fourth section of the amendment requires such determinations to be made jointly by the vice president and the cabinet, with the vice president immediately assuming the position of acting president. The amendment also details how the president may reassume the office from the acting president after a declaration of inability.