It's been a long time since we had an incumbent president who actively campaigned for the person he wanted to succeed him. Teddy Roosevelt pushed hard for William Howard Taft, and then regretted the hell out of it thereafter, and even tried to beat him four years later. Eisenhower held Nixon at arm's length, the way you carry a snake, as any reasonable person would. Hubert Humphrey had to spend three months running all the way from LBJ. (This had the added drawback of being part of why Johnson sat on the recorded proof of Nixon's treachery regarding the Vietnam Peace Talks in Paris.) Nixon was gone by 1976. Jimmy Carter only had one term. Ronald Reagan was cognitively functional for about three hours a day when George H.W. Bush ran to succeed him in 1988. Al Gore stupidly benched Bill Clinton, and C-Plus Augustus was a harborless plague ship drifting through the campaign in 2008.