However, it is a fallacy to say this is a "Christian nation" founded by "Christianity." Some of the most notable of the founders were NOT Christian. However, they WERE believers in God, however He might be defined. One cannot say the founding of this nation was SECULAR, but one would equally be erroneous to say it was CHRISTIAN.
This may be technically true. But I think it's also fair to note that the concepts enshrined in our founding documents -- especially the DOI -- basically developed out of a Christian tradition in general and the Protestant Reformation in particular.
The US founding was a product of the Age of Enlightenment, which was certainly the product of a Protestant Christian perspective. Is is impossible to imagine a similar set of ideals occuring in any society other than a Christian one, and in fact history shows that this did not ever happen.