Nixon wasn’t convicted.
Interesting here(from wiki)...Maybe it’s the same reason Sydney begged Pres. Trump not to pardon Gen Flynn...
“After Ford left the White House in 1977, he privately justified his pardon of Nixon by carrying in his wallet a portion of the text of Burdick v. United States, a 1915 U.S. Supreme Court decision that suggested that a pardon carries an imputation of guilt and that its acceptance carries a confession of guilt.”
OK, thanks for the info.