MSNBC:
The Twelfth Amendment to the Constitution says the presidential electors "shall meet in their respective states, and vote by ballot for President and Vice-President, one of whom, at least, shall not be an inhabitant of the same state with themselves….”
The effect of this provision is that a presidential candidate and his or her running mate must reside in different states.
Sen. Clinton and her husband are both residents of the same state. A Clinton-Clinton ticket would risk forfeiting all of New York’s 31 electoral votes. (He could quickly re-locate to Connecticut — only 12 miles from the Clintons' home in Chappaqua, N.Y., but that would seem a bit fishy, wouldn’t it?)
If elected president, Hillary Clinton could in theory appoint Bill Clinton to serve as vice president — but only if there were a vacancy in the office of vice president.