Christian nationalism holds that the US was founded on "Judeo-Christian" principles. "Judeo-Christian" seems nonsensical to begin with (Judaism is Judaism because it rejects Christianity and vice versa). Regardless, principles in the holy texts of Judaism and Christianity are so distinctly different than those embodied in America's founding documents that to suggest a link between them is to grossly misrepresent America.
Rather than waste time defending against arguments that might not be used, I leave it to proponents to define "Judeo-Christian principles" and provide arguments. Perhaps, each respondent may limit themselves to one or two of their best arguments, and let's do our best to keep it civil folks!
FYI, there is an identical post in the religion section should anyone feel their arguments would be more appropriate there.