Phyllis Tickle interviewed in the Wittenburg Door:
“Christian nation” is such an offensive term that I can hardly speak it, even. One of the biggest blows to Christianity’s vitality and legitimacy occurred on the day that Constantine made it the official religion of the Empire. Nobody in his or her right mind would want to be a member of a socially acceptable religion. It’s very dangerous for the soul. A nation is in the business of doing Caesar’s work, not God’s. There’s a distinction we get from the New Testament between religion and politics. That’s not to say, however, that one shouldn’t vote according to one’s personal beliefs. All of us do that. But it is to say that one should never expect the state to function in accord with passionate faith. It won’t. It can’t. It shouldn’t.
I don’t recommend much of anything else in the article, but that section jumped out.