I would say there was a level of corruption in politics in the 20 years prior to Nixon's second run for President. Such things as the shady vote count when Johnson won his Senate seat. Or the Nixon-Kennedy election, Of course all of these are allegations and never proven in a court of law.
"A study of Lyndon B. Johnson provides new evidence that the 36th President stole his first election to the United States Senate, in 1948...Mr. Caro maintains that although ballot fraud was common in the late 1940's in some parts of Texas, the Johnson campaign of 1948 raised it to a new level. Mr. Caro supports his charge with an interview with Luis Salas, an election judge in Jim Wells County who said he acknowledged his role only after all others involved in the theft had died." Source: NYTimes
Another well known instance of (alleged) corruption was JFKs win over Nixon.
"But historian Robert Dallek, who wrote definitive biographies of JFK and LBJ,, concluded that Daley’s storied political machine “probably stole Illinois from Nixon”—though he reminds readers that Kennedy “would have won even without Illinois.” FBI agents who had placed wire taps on key Daley lieutenants (for entirely unrelated purposes) also had reason to believe that Illinois was rigged." Source: Politico
And this doesn't even get into pre-ww2 elections where there are plenty of alleged instances of outright voter fraud, intimidation, and the like.
If you have the time to read, please check out this article, that talks a bit about the EH Crump political machine in TN. GI's fresh back from the war tried to run a legit campaign and were totally cheated. They reacted like any fresh soldier would and laid siege to the town and basically initiated what would now be called a local coup d'etat that ended in deaths and explosions and the works. It is a fascinating piece of history.