I can't remember an incumbent ever campaigning for his desired successor to this degree.
Bush for McCain - no,
Clinton for Gore - no,
Reagan for Bush - no
Johnson for Humphrey - no,
Eisenhower for Nixon - no,
Truman for Stevenson - no,
Coolidge for Hoover - no,
Wilson for Cox - no,
Roosevelt for Taft, perhaps,
Cleveland for Bryan, not even close.
If anyone can think of an incumbent President ever campaigning anywhere close to this level of intensity, please chime in!
This is misleading. George W. was enormously unpopular in 2008 and would have been a liability for McCain, perhaps more so than Palin was. In 2000, Gore was unhappy with Clinton for his personal mishaps and hoped to separate himself from him because of this. H.W. appeared with Dole a handful of times, as did Reagan for Bush: keeping in mind Reagan was 76 by 1988 and dealing with Alzheimer's. As with the W. scenario, Johnson would have been a liability for Humphrey. Eisenhower did, actually, campaign for Nixon towards the latter end of the '60 Campaign.
Once you move beyond the 60s, you're dealing with an entirely different political reality.
