On February 10, 1967, the 25th Amendment to the US Constitution was ratified.  As any fan of “24″ knows, the 25th Amendment mandates that the vice president become president when there is a vacancy or when the president is disabled, resigns, or is convicted on impeachment charges.

Here’s a link to the a full version of the Amendment – http://www.ushistory.org/documents/amendments.htm#amend25