(CNN)Here is some background information about the line of succession for the president and vice president of the United States.
Article 2, Section 1, Clause 6, Constitution of the United States: In Case of the Removal of the President from Office, or of his Death, Resignation, or Inability to discharge the Powers and Duties of the said Office, the Same shall devolve on the Vice President, and the Congress may by Law provide for the Case of Removal, Death, Resignation or Inability, both of the President and Vice President declaring what Officer shall then act as President, and such Officer shall act accordingly, until the Disability be removed, or a President shall be elected.
1. Secretary of State
2. Secretary of the Treasury
3. Secretary of Defense
4. Attorney General
5. Secretary of the Interior
6. Secretary of Agriculture
7. Secretary of Commerce
8. Secretary of Labor
9. Secretary of Health and Human Services
10. Secretary of Housing and Urban Development
11. Secretary of Transportation
12. Secretary of Energy
13. Secretary of Education
14. Secretary of Veterans Affairs
15. Secretary of Homeland Security
1792 - The Presidential Succession Act passes, making the Senate president pro tempore next in line after the vice president to succeed the president.
Section 2 of the 25th Amendment of the US Constitution: Whenever there is vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take office upon confirmation by a majority vote of both houses of Congress.
Seven vice presidents have died in office: George Clinton who served under both Thomas Jefferson and James Madison; Elbridge Gerry who served under Madison; William R. King who served under Franklin Pierce; Henry Wilson who served under Ulysses Grant; Thomas Hendricks who served under Grover Cleveland; Garret Hobart who served under William McKinley; and James Sherman who served under William Howard Taft.