The big problem is Bill.
Who would want to be Vice President if Bill Clinton were the husband of the President? That would be an intolerable position.
Second, who would want Bill Clinton as husband of their Vice President? Another intolerable situation.
And, I guess it's reasonable to ask, who wants Bill Clinton around anymore anyway? I certainly wouldn't miss him if he were gone.
Another factor is that Hillary and Barack really don't like each other. However, that didn't stop JFK and LBJ in '60.
Arf