Reagan didn't help campaign for Bush because his health was already rapidly deteriorating.. Eisenhower didn't really campaign for Nixon either. FDR and JFK died before they could do anything. Gore pushed Clinton away despite having high favorables. Both Bushes, Carter, Ford, LBJ, Nixon, Truman all had bad favorables going out of office. This is going to be something we haven't seen in possibly 100 years. I'm excited.
