I only watched Imus once and he was saying the Swift Boat vets were drunks and should be killed (paraphrased); it was some time ago. Never watched him again.
Before this year, Imus was pretty much like O'Reilly. He never went in the tank for either side. In 2000, he backed Dubya, and stood for Hitlery! until he went into the voting booth and voted for Rick Lazio. He admitted on the air that he couldn't bring himself to vote for the Witch.
Also, they probably still have it in the archives, there was a hillarious interview between him and Bush the Elder that year, with GHW Bush really getting the best of him.
I think that Imus doesn't really have a core, but is simply driven by the latest fad, and will say his usual spiel in support of his cause.