America as Christian?

Ben Witherington gives a very thought-provoking post on how we should think of America's "Christian" foundations. I head many talk about how Christianity was the foundation of Declaration of Independence and Constitution. However, I have serious doubts that much of what we read was based on the Bible. Perhaps it was informed by biblical principles, but not founded on them. I am not well-learned enough to fully engage with his post , but my interest is definitely peaked by his thoughts [with a modification in the first comment below the post, I absolutely deny the second comment...for the record, I would like the man to give a better philosophical explanation of things for those desirous in Edwards (though he is obviously fallible)].