Nowhere in the
United States Constitution does it say that you have to vote for a
President and a
Vice President from the same
political party. Really. The two offices are completely separate during the
election process.
Not that a party split between these two offices has ever happened in U.S. history, but I think it'd be a kick if it did someday. Think it's difficult to get anything done in Washington, D.C. when you have a Democratic President and a Republican Congress? How about if you had a Republican President and a Democratic Veep?