How did his pardon of Richard Nixon affect Gerald Ford's political standing?
It cost him the 1976 election.
Few people didn't understand that when Ford pardoned Nixon in 1974, it was part of a deal. Without agreeing to do this, Ford would not have succeeded Spiro Agnew as VP and become the nation's first completely unelected president.
The 1976 election was rather close--50.1% for Jimmy Carter and 48% for Ford. Many polled voters said outright that the Nixon pardon was their main reason for voting for the Democrat (although since this was the first election after the Watergate hearings, any Republican would have been a hard sell).
The only thing that kept Ford from a second term was also the only thing that got him his first term, so there aren't many compelling "What if?" moments here. His brief term had few controversies and he was not, prior to becoming VP, a well-known national figure.