I have a feeling that Colbert isn't really a lefty. I think I have him pegged as a Dem with Libertarian-ish tendencies. He's mentioned RP quite a bit and in a very favorable way (by acting like a NeoCon himself).
Now, I think Stewart is a Dem or leans that way, but in recent interviews, it seems like he has been listening to some of RP's positions.
The Alan Greenspan interview was VERY revealing, I thought. As someone who is fairly new to terms such as "The Fed" and "free markets" and stuff like that, Stewart's questions were very insightful and showed considerable thought. I don't think that Greenspan wanted to admit that the US is not really a "free market economy" and I hold Stewart in a higher level than I originally thought. He might be an RP convert in due time, they both could.
Or, maybe I'm just dreaming. I always wish that guys like Stewart/Colbert would come right out and say "we support RP." Yeah, that would pretty much seal the deal....