Sophia McClennen says Stephen Colbert gets lower ratings among Republicans because they just don't get his humor:
It is the socially conservative, less educated, Tea Party version of the GOP that is least likely to want to watch smart comedy like Colbert’s. This is the portion of the population that thinks climate science is a liberal plot, Obama is not a citizen, and the separation of church and state is a myth. As Chris Mooney explains, “liberals tend to be more open, flexible, curious and nuanced—and conservatives tend to be more closed, fixed and certain in their views.” It’s not surprising that those differences would also yield different tastes in comedy.Read McClennen's full piece here.
This means that it is not just a question of who Colbert targets in his joke; it is also a question of how he makes the joke itself. Nuance, irony, and layered thinking may be more of the problem than Trump jokes. He has virtually abandoned jokes about Fox News but clearly that isn’t enough to attract GOP viewers.