Letterman's always been completely open about his contempt for the stupidity on the right.
he tore mccain apart when mccain lied to his producers and said he had to cancel because he was going to be in another state, and then he took time to do an interview with katie couric at the same time he was booked to be on letterman. Letterman put the live feed of the interview on his show and called Mccain out on it. McCain was a punching bag for 2 months after that. Letterman took full credit for sinking Mccain's campaign when he lost. hilarious.