I'd pick Nixon as one of the worst...not that he didn't make some adroit foreign policy moves...he did. His deep negativity, personal vindictiveness, and paranoid attitude, however, rendered him absolutely unfit for office...and resulted in his eventual resignation. He'd have been impeached if he hadn't resigned, and rightly so.

G.W. Bush was one of the worst too, but not near as bad as his V.P. I think it was Cheney who was really running the show and Bush was out front like Charlie McCarthy (the puppet). In a more perfect world Cheney would be tried for war crimes, but I think Obama is quite wise not to push for that. It would only create a huge partisan mess that would distract people from doing something positive instead at a very crucial time of financial crisis.