I don’t recall any Democrat actually resigning over sexual misconduct. I remember when MA Rep Gerry Studds (his actual name) plied male pages with some kind of cranberry juice alcoholic cocktail and had sex with them. He was censured, but went on to be reelected until he retired.
Probably cost him the Dem nomination for president in '88. Hart just returned to the senate, finished his term and didn't run again.