Colbert's trying to be funny turned out to be a struggle in futility. Grope and grasp as he did, his 'program' sank faster and lower than the Poseidon. It wasn't pretty. It wasn't funny. Colbert should be embarrassed at his woeful performance.
Colbert's done. He doesn't know it yet, but he's done not because he did this to Bush, but because he did it at all. Presidents come to these dinners because they're gloves-on and good-hearted ribbing is the norm, like a Dean Martin "roast." Colbert betrayed the whole gig, and honorable folks know it. So ... Colbert's done. He just put up a glass ceiling for himself.