What does it mean that the US is a Christian nation?

The idea of the separation of church and state was actually pushed through as constitutional law by Baptists. Baptists were against any form of state influenced religion or state sponsored religion. Baptists believe in freedom of conscience, to believe or not believe in God and to choose to worship or not worship according to personal choice. Baptists, a large portion who are "fundamentalist" are the ones that provided your religious freedom.