The government of the United States is not founded on the Christian religion, but that means, narrowly, the central government. The most definition statement of separation is found in Article 6, which says that no religious test shall be required to hold office. Nothing like the Test Act of Great Britain, which barred Catholics and Jews from office until it was repealed in 1828. But separation of church in state under American law is always defined in a negative way. We do not have a state church. Bishops do not sit in Congress. One does not have to communicate in the state church to hold public office. Our republic is NOT the divine right monarchy that Great Britain was, with the king being the local version of Constantine. To go beyond that is to assert that our government must ignore the plain fact that our society, indeed our common law, isfounded on Christian principles. There are those who think that we have put those principles on a non-religious footing, but that is merely a claim, a sectarian view, the view of the ten percent of our people who say they have no religion. This is not France, where that number is a much greater part of the whole,
Of course you can provide documentary proof for that.
The founding fathers came to the task of creating a new government from the experience of religion, its persecutions and wars in Europe. The colonies, themselves were not of one accord in belief or practice. Throw into this mix the Enlightenment and contact with native American thought, and you have a very diverse group with a common goal of forming a government that works for all. This is not to ignore the theological belief of citizens, but to respect that each has the right to his belief and no religion or sect has prominence over another.
We accomplish this by giving the greatest possible freedom to the individual to choose how he will live his life with as few laws as possible governing personal, "moral" behavior. For instance, the Bible forbids charging interest on loans to the poor without regard to whether the loan will ever be paid back or not and yet our laws allow rates of interest for poor credit risks that are clearly condemned. We accept that. Why then should we rail against abortion that is clearly allowed and even required under certain circumstances in Jewish tradition by creating a law against it? As long as we don't pass a law requiring abortion, we are allowing religious freedom.
So the laws should remain minimal while each of us, according to our own religion are held to a higher standard.
You might want to do some research on the Iroquois confederation and the influence it had on the structure of our government.