A lot of people are saying that Pres. Gerald Ford lost the 1976 election because he pardoned Pres. Richard Nixon. It is true that the election was extremely close, and Ford could have won with about 10k more votes in Ohio and Hawaii.
But there are probably dozens of factors that similarly influenced enough voters to possibly shift the election. For example, appointing Nelson Rockefeller VP, continuing with hated Nixon cronies like Henry Kissinger, breaking his promise not to run for reelection, allowing S. Vietnam to fall to the commies, proposing to slow inflation with his ridiculous Whip Inflation Now buttons, making political gaffes like saying the commies don't dominate Poland, letting Jimmy Carter get all the Southern and evangelical voters, giving the appearance of being a dumb football player who is in way over his head, having an unstable wife, etc. We expect a president to lose when he loses a war and lets the economy tank. The amazing thing is that the 1976 election was as close as it was.
While everyone agrees that Nixon was a bad guy, less than 10% of the population can describe the crimes for which he was being impeached. Perhaps Ford should have just declined to prosecute Nixon. Ford was the Chief Executive, and has the authority to make the final call on who is or is not prosecuted by the Justice Dept. Maybe Ford was worried that he would be impeached for it, because Nixon's main crime was a failed attempt to impede the DoJ investigation of the Watergate burglars.
Pardoning Nixon also ended the official investigation of him. I guess the difference between Ford's obstruction of justice and Nixon's was that Ford was transparently using his presidential authority, and Nixon was being sneaky. Nixon was Tricky Dick, and Ford was just dumb. We think that Ford was telling the truth when he explained his reasons for the pardon. A lot of people suspected that he wasn't telling the whole truth, but I doubt that it really cost Ford very many votes.