I don't think many Christians would disagree with his statements. Assuming you believe in God and Satan of course.
"Satan is attacking the great institutions of America, using those great vices of pride, vanity, and sensuality as the root to attack all of the strong plants that has so deeply rooted in the American tradition."
Would you disagree that our society is becoming increasingly vain, prideful, and sensual? Seems pretty common sense to me.
"This is a spiritual war. And the Father of Lies has his sights on what you would think the Father of Lies would have his sights on: a good, decent, powerful, influential country - the United States of America. If you were Satan, who would you attack in this day and age?"
This makes it seem like the US is the only place being attacked by evil which is a ridiculous notion, but the US is still under spiritual attack (if you believe in that sort of stuff)
"We look at the shape of mainline Protestantism in this country and it is in shambles, it is gone from the world of Christianity as I see it."
Christianity in general is crumbling in the US. It is starting to follow the European model in which churches are social clubs. Once they become a social club the foundation shatters and pretty soon you have tourist attractions instead of churches.
Colbert 'reported' on this story last night, and I guess I didn't see the big deal. Santorum is a Christian. Are we that surprised that he believes in the devil, and that he believes that the devils is active in the US? Now Santorum does make it sound like the US is the only place where the devil is attacking, and that the rest of the world is living on easy street which I would happen to disagree with, but other than using the quirky term 'Father of Lies', I am not sure why this story is such a big deal.