It is all political humor favoring the left based on the shows, hosts and networks.
Colbert's show is less than six months old and still finding an audience, but then again, as successful as Letterman was, Leno consistently beat him in the ratings as the 2 shows are still up against each other with different hosts.
The game has changed with dvr's. I wonder if the ratings are based during the time people watch during the air times or if they also measure people who watch later on their dvr's and other streaming services.
Fallon is too liberal for my tastes and too lame and corny. Colbert is indeed sophisticated and intelligent and really doesn't bother me too much.
He has done a lot of Trump bashing lately but not to be taken too seriously as these shows cater to political humor. Trump gave it back to Hillary and called her a liar. So glad to see him say that. RI much prefer Ted Cruz and I'm glad he's making gain right now. If Trump and Clinton ran against each other, I think he would destroy her.
I don't think the ratings matter much in late hnight talk shows anymore. The hosts are all friends with each other and the networks are all getting their share. As much as I like Colbert, he and the others cater mostly to the left and it is what it is. I still find his presentation entertaining and hardly watch Fallon. Recent exceptions were Bruce Springsteen and Tina Fey. I will watch any talk show if there is a guest I like, but with Colbert, I watch every episode. The only guest so far that annoyed me was Bill Mohers.