The United States presidential line of succession is the order in which officials of the United States federal government discharge the powers and duties of the office of President of the United States if the incumbent president becomes incapacitated, dies, resigns, or is removed from office (by impeachment by the House of Representatives and subsequent conviction by the Senate) during his or her four-year term of office. Presidency succession is referred to multiple times in the U.S. Constitution – Article II, Section 1, Clause 6, as well as the 12th Amendment, 20th Amendment, and 25th Amendment. The Article II succession clause authorizes Congress to provide for a line of succession beyond the vice president, which it has done on three occasions. The current Presidential Succession Act was adopted in 1947, and last revised in 2006.
The line of succession follows the order of Vice President, Speaker of the House of Representatives, President pro tempore of the Senate, and then the eligible heads of federal executive departments who form the president's Cabinet. The Presidential Succession Act refers specifically to officers beyond the vice president acting as president rather than becoming president when filling a vacancy. The Cabinet currently has 15 members, of which the Secretary of State is first in line; the other Cabinet secretaries follow in the order in which their department (or the department of which their department is the successor) was created. Those heads of department who are constitutionally ineligible to be elected to the presidency are also disqualified from assuming the powers and duties of the presidency through succession. Since 1789, the vice president has succeeded to the presidency intra-term on nine occasions, eight times due to the incumbent's death, and once due to resignation. No one lower in the line of succession has yet been called upon to act as president.
Widely considered a settled issue during the late 20th century, the terrorist attacks of September 11, 2001 demonstrated the potential for a decapitation strike that would kill or incapacitate multiple individuals in the presidential line of succession, in addition to many members of Congress and of the federal judiciary. In the years immediately following the attacks, there were numerous wide-ranging discussions in Congress among academics, and within the public policy community about continuity of government concerns, including the existing constitutional and statutory provisions governing presidential succession. These discussions are ongoing. One effort, that of the Continuity of Government Commission, a nonpartisan think tank, produced three reports (in 2003, 2009, and 2011), the second of which focused on the implicit ambiguities and limitations in the current succession act, and contained recommendations for amending the laws for succession to the presidency.