Actually, he did deride McCain often on his show. And, when Congress had ended its session earlier this year and the Republicans declared they would stay even "in the dark", he publicly kept saying I have little faith they will do anything. He also considered voting third party for a long time, actually having Barr and Paul on his show. I think he believes most Republicans have lost their way, but that there are some good examples.
On foreign policy, I can understand his hesitation. It is a huge jump for somebody to make, and the fact he hears the other side and lets people talk(unlike Lou Dobbs' show I may add) is a huge step. He definitely isn't like the type who shut down opposition. His views have adjusted to accomodate a big tent is all. You won't hear him saying Ron Paul isn't a true Republican at least.