I've wondered if Stephen Colbert is truly a right winger and this is a stunt to make McCain more palatable to voters.
If so, it's the latest in a long line of coverage, much of it documented by Media Matters for America, showing how McCain consistently gets a free ride in the U.S. media. If there is any doubt about that, go here: http://mediamatters.org/issues_topics/john_mccain?f=h_hot

There are two Stephen Colberts. One is an actor with well-known liberal views, and the other is a character satirizing right-wing pundits (especially Bill O'Reilly). But sometimes Colbert slips out of character and says things (like this comment about John McCain) that leave little doubt about where he really stands.