I think there may have been real damage to Trump last night.
What is Trump's big selling point? It's him. It's his personality. It's the idea that he is not an ordinary human being. He's super wealthy and super competent. It's him, and only he can fix the horrible state of this country.
Last night he looked awful. Whiny. Lying. ("I never said that") Generally unlikable and not in command of his facts, his feelings, or the general state of the debate. In his post debate analysis he seemed even more whiny. (Did anyone catch the "I had a bad microphone" complete with "I don't know if it was set up that way"? Pathetic.)
So all he has is himself to sell, and his product didn't look very good last night.
He'll still get a good share of the vote. He is still the fairly solid Republican. He's still pro-business, anti-regulation, cut taxes and pretend that doesn't affect the national debt candidate, so most Republicans will vote for him. However, when it comes to core values and ideology, he isn't as strong as Romney. He'll pick up some Hillary haters, but there are plenty of Donald haters who would otherwise vote for a Republican to offset those. Given all that, I just can't see him making up any ground above where Romney got, barring some unforeseen and strange event in the next 41 days.