Christian Nationalism is political ideology that asserts the US government is defined by Christianity and it should actively preserve and promote it. The Constitution is a secular document that makes no mention of any specific religion and explicitly rejects religious privilege within the 1st amendment:
“Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof [...]"
Christian Nationalism and the Constitution of the United States are at odds, but the latter has authority being the law of the Land. Christian Nationalism rejects the constitutional principle of a secular state and is fundamentally at odds with core American democratic principles.