True, but it is relevant to whether we call them Christian principles.Whether the principles predate Christianity is irrelevant to the question of whether the union was founded on those principles.
Which principles that you called Christian do you consider to have been used to craft the US Constitution and the American government? That man is fallen? Jesus is the only salvation? God is a trinity? Blessed are the meek? To repent sin?Those who did the founding obviously thought they were Christian principles, which they were.
Or perhaps you meant biblical principles of governance, such as man ruling the wife, masters ruling slaves, kings ruling subjects, and the deity ruling all of them? Was America founded on those principles -?
Or maybe you meant biblical law such as rest on the Sabbath, honor your parents, and have no false gods?
The principles that America was founded on include limited government (divided with checks and balances, transparent), secular government, representative democracy, personal rights and individual political freedom, laissez-faire economics and free enterprise, egalitarianism, and the like
Where is the overlap?