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!
Bush -- extremely unpopular
Clinton -- somewhat unpopular with independents; Gore erred on the side of caution
Reagan -- not in good health; did not have a good relationship with GHWB
Johnson -- extremely unpopular
Eisenhower -- would have hurt his "transcending politics" image
Truman -- unpopular
Earlier cases predate the "modern" presidential campaign and aren't good for comparison.
