Q. I know the Vice President takes over if the president dies or can’t finish a term, but what if something happens to the Vice President? Who’s second in line and third in line?
The Speaker of the House of Representatives is second in line, and the President Pro Tempore of the Senate is 3rd in line. The current Speaker of the House is John Boehner, a Republican from Ohio. The current President Pro Tem of the Senate is Orrin Hatch, a Republican from Utah. (You never hear much about the President Pro Tem of the Senate because the post has limited duties. However, the position is usually occupied by the US Senator from the party in control of the senate who has been in the Senate the longest.)
No Speaker of the House or President Pro Tempore of the Senate has ever actually become President of the United States. It is also worth mentioning that when a Vice President has to become President, this does NOT mean that the Speaker of the House moves up to be the new Vice President. The new President would appoint the new Vice President, with confirmation from Congress.
Probably the most interesting succession situation in history involved the administration of Richard Nixon. Nixon’s Vice President, Spiro Agnew, stepped down from the post in 1973 and Nixon appointed Gerald Ford to take his place. When Nixon himself resigned in the wake of the Watergate scandal, Ford, who was originally not in the line of succession at all, was suddenly President of the United States.