It seems absurd in retrospect, because I was only 10 years old in 1968 (although my prodigy status had gotten me into the 8th Grade), but I was very attracted to Eugene McCarthy's campaign. Had he or Scoop Jackson ever won the presidency, people like myself might well have remained Democrats.
McCarthy was an original. This article is fairly comprehensive. But to capture the mood of the time, you should read the James Jackson Kilpatrick write-up of that campaign in the National Review.