Is the USA a “Christian nation”? Depends on what you mean by that, I suppose. But its origin in Judeo-Christian principles is clear, based on founding documents, acts of congress and presidents, and the writings of the founders. The recognition and celebration of that heritage has been nearly universal among US national leaders until very recent times. You can decide if that was a good thing, or a bad thing, but you can’t pretend it is a non-thing.