He said atheism.
I believe the nation was founded on a belief in God, not a label like 'christianity'. I think the 'christianity' label just compartmentalizes people and separates them instead of unifying them under the One God.
Jesus said, "I am the way, the truth, and the light, no man comes to the Father except through me." Jesus didn't come to establish some mealy-mouthed milktoast "religion" so everyone could "get along", He came to save man from sin.