In no way is America founded on Christian principles, but rather Greco-Roman political philosophy revived during the Renaissance and the Enlightenment—a time in which, not coincidentally, the Church's stranglehold on the social and intellectual freedom of Western Civilization finally began to slip. Most of the Founding Fathers were Deists; an Enlightenment quasi-religion which bears only a superficial resemblance to Christianity.
Don't believe me? Open up your Bible and turn to the passage about democracy. Oh, I'll make it easier. Turn to a passage about any form of representative legislative government. Oh? Can't find any? Not even one?
I rest my case.
However, there is Romans 13:1-6, which explains in detail why the rule of a king is never to be challenged. By that passage, the American Revolution was a direct attack on God's authority. So be it, says I.
Personally, as a true child of the Enlightenment, I'm too fond of my own social and intellectual freedom to want yet another religious zealot in the White House. Didn't the one we have now do enough damage? No more backsliding into medievalism, please. Have your faith, follow the spiritual path you choose and practice it as fervently as you wish. I swear that I will never challenge your right to do these things of your own free will. But if you attempt to force your faith on me, as you Christians have the unfortunate tendency to do whenever you have power, then it's war.