Nixon resigned in order to spare the country the spectacle of an impeachment and removal from office, which the votes were there for.  I might suggest reading up on the history of how that all went down before crowing that only 2 Democrats were ever impeached.  Nixon certainly would have been but the A mix of Dems and Republicans met with him to convince him to resign rather than be impeached and removed from office.

https://en.wikipedia.org/wiki/Richard_Nixon