It is the single greatest scandal to have ever touched the office of the President of the United States: Richard Nixon was impeached by Congress. Which is to say, he was charged with criminal offences related to his office. More specifically, the charges related to his role in the Watergate scandal and its attendant (and failed) cover-up.
In little more than a fortnight, Nixon would resign the Presidency in shame, and his hand-picked successor would immediately give him the quid pro quo of a pardon that also covered Nixon for “crimes yet to be discovered.” This allowed Nixon to avoid actually facing the charges against him, and made him one of the few people to have been pardoned for crimes he was never convicted of, or even tried for; and also did untold damage to the institution of the Presidency, which would never again be as respected as it had been before 1973.
All My Heroes Are Dead — Dar Williams