Pizzaboy above said it better than I could.
Also notice how I said this country has always been a Christian nation in the sense that most of it's citizens have always been Christian.
As for Dennis Prager, I would highly recommend him and his radio show to anyone, conservatives or liberals. He isn't a big mouth hack like Rush, Hannity, etc. The guy is extremely intelligent and well spoken. Even a lot of liberals listen to him, even though they may not agree with him often.