Carlson claimed Stewart is a "partisan hack" who is so popular that no one dares to criticize him. And that's frustrating Carlson.
If this is the case, then the two do have a lot in common.
Everybody knows what happens if you are a Republican (with standing) and say anything negative about Rush.
He'll call you on it. You get concerned. You apologize. The DNC mocks you on a website. Chris Matthews, Rachel Maddow, and Keith Olbermann all laugh (at you, not with you). And pundits start writing your political obit.