I have to say, I don't understand the idea that one would separate one's faith from one's politics.  For an agnotheist like me, all this means is a pretty healthy skepticism of prayer in schools.  But if I did have a firm belief in God, I'd have a hard time reconciling the following two principles:

1. There is an omnipotent, omniscient and omnibenevolent deity, and man's highest destiny is to fulfill His purpose
2. I routinely ignore what this deity says because my neighbors disagree

I can't see how you can have any sort of meaningful faith and divorce it from your voting decisions.  Religious faith is supposed to tell you, among other things, what is right and wrong.  How are you supposed to vote without reference to your notions of goodness?

America, and to a lesser extent other western nations, have a long history of keeping doctrinal disagreements out of the public square, an excellent notion.  But my reading of political history, admittedly incomplete, does not indicate that our predecessors actually thought that people were supposed to vote entirely without recourse to their relgious faith--that the Almighty God was supposed to be kept in a dark corner of your heart where he couldn't possibly affect any public portion of your life.

Indeed, some of the noblest endeavors in American history, like the fight against slavery and the civil rights movement, were very explicitly religious movements, and wouldn't have succeeded half so well without the power of the church behind them.  Though I don't share their faith, I'm totally okay with that.  Believers will believe.  The rest of us will have to judge their beliefs by our own lights, of course.