John McCain's selection of Alaska Gov. Sarah Palin as his vice presidential running mate has so far generated more discussion about her family dramas than her potential position as being a "heartbeat away from the presidency."

Since 1960, two vice presidents have assumed the presidency — Lyndon Johnson after John F. Kennedy was assassinated and Gerald Ford after Richard Nixon resigned. Less known is that George H.W. Bush served as acting president during the Reagan years, and Dick Cheney has twice been acting president under George W. Bush (no jokes from the left side of the peanut gallery, please).

According to the Constitution's 25th Amendment:

"Whenever the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that he is unable to discharge the powers and duties of his office, and until he transmits to them a written declaration to the contrary, such powers and duties shall be discharged by the Vice President as Acting President."

The elder Bush took over on July 13, 1985, when Reagan had surgery for colon cancer; Bush's "term" lasted about eight hours. Of course, Reagan was also hospitalized after a failed assassination attempt on March 30, 1981. Bush was essentially the acting president at that point despite the famous pronouncement by then Secretary of State Alexander Haig that he was "in charge" while the vice president was aboard Air Force Two flying to D.C. However, since the president was still alive and had not handed over power in a written form, the legality of Bush's acting presidency could have been called into question.

Cheney's two "terms" also centered on matters of the colon. On June 29, 2002, he served a little over two hours while the younger Bush had a colonoscopy, and five years later, on July 21, 2007, he has another two hours with his finger on the button for another presidential colonoscopy.

Given John McCain's age — older than Reagan was when he assumed office — should the GOP retain the presidency it seems quite possible that Palin will see some action at acting president during her boss's routine medical procedures.