It was clear to the left that Richard Nixon’s victory in 1972 could have realigned American politics. Many blue collar unions supported him and helped him carry New York.
He had to be stopped by any means necessary.
It helped that effort that his WH (for whatever reason) perpetratred the Watergate break-in, and that he, after finding out about it, authorized and coordinated obstruction of justice in the form of payoffs to keep those arrested quiet.
If you have enemies like Nixon had, you need to be squeaky-clean. Nixon wasn’t.
Trump, however, IS.
Nixon's great crime was winning by a nationwide 49 state landslide. No one in the media voted for him and they did not know anyone who did. He clearly must have stolen the election and had to be punished.