Richard Nixon felt he was cheated in 1960 (he wasn’t really, but the election was indeed extremely close) and he was the cheater himself in 1968, it just gets less press than 72. Nixon was running opposition to a widely unpopular Lyndon Johnson’s Vice President (Hubert Humphrey) because even though Johnson could run again, the prospect of doing so was futile. There was a peace agreement being written for Vietnam right before that election which would have taken an already close race and completely pulled the monkey off the democrats back. Nixon had his staffers throw a wrench in the deal which was intercepted by the NSA. Johnson was furious in private, and said that Nixon was killing kids, but did not bring it to the public for fear of what would happen with that information beyond just political points. It never got out and Nixon crushed Humphrey.

Basically, Nixon had a chip on his shoulder for years and ran a dirty paranoid administration to avoid close calls, and that had proved to be an extremely fruitful strategy for him in the past.