Close but no cigar. Any politician can quit at any time for any reason. LBJ announced in March of 1968 that he would not run for another term though he was in the middle of doing just that.
Calvin Coolidge told the press that he would not run for another term though he looked to be a sure thing. The death of his son had a lot to do with his decision.
Other presidents like Andrew Johnson just let the clock run out without doing anything. What we call "Retired on active duty" or R O A D.
Richard Nixon was not impeached. He resigned which is just a fancy word for quitting. Would he have been impeached? The two special prosecutors Cox and Jaworski both said that they didn't have the evidence to get a conviction if the trial was legitimate and not a political Kubuki dance. Nixon was forced out by the GOP. Unlike the democrats, the GOP went down the street to the White House and said we can't support you. It's time to go.
http://watergate.info/impeachment/im...articles.shtml This link goes to the articles that passed the committees but was never brought to a vote in the full house. Which is where the impeachment (indictment) takes place. If impeached then the trial occurs in the Senate.
By the way, Gerald Ford was not an idiot as someone said. He was a lawyer, a navy pilot, a member of the Warren Commission, a ranking member of the GOP in Congress, and before he became president a highly respected member of that body.