25 amendment
The Speaker Of The House
The first successor, the vice-president, is set by the Constitution. The rest of the list was set by an act of Congress. An amendment to the Constitution provides for a method of filling a vacancy in the vice-presidency.
second in line
It determined the order of succession.
The Chain of succession for the US Presidency is:Vice-PresidentSpeaker of the House of RepresentativesMembers of the Cabinet in order of Departmental Seniority
http://wiki.answers.com/Q/What_is_the_entire_order_of_succession_to_the_presidency_if_he_or_she_should_die"
United States Code Title 3 Chapter 1 Section 19
The order of succession is: (1) Vice-President, (2) Speaker of the House,(3) President Pro-tempore of the Senate,(4) Secretary of State, (5) Secretary of the Treasury.
If you are talking about who succeeds the President in office, then the phrase commonly used would be "succession order," which was established in 1947 when President Harry S. Truman signed the Presidential Succession Act.
As of now, Kamala Harris is the woman who has come closest in the presidential succession order to the office of the president of the United States. In her role as the Vice President, she is next in line to assume the presidency if the President is unable to fulfill their duties.
The 25th Amendment to the Constitution was necessary to provide for the order of succession if something happened to both the president and vice-president. Article II of the Constitution didn't provide a definitive succession past the first two officials. The amendment was adopted on February 23, 1967.