This topic has been debated ad nauseam.

To begin, it seems that Christian Nationalism has little in common with Christianity, including Christian ideals that have to do with compassion, the common good, loving one's neighbor, and so on. Christian Nationalism seems to be a movement about overthrowing the US Constitution and imposing fascist ideals on the American people. This is pretty clear in the Christian Nationalist rhetoric and manifesto.

Christian Nationalists do not think twice about making people suffer, and this includes women as a whole. There is no concern for women who are raped, even in the case of incest and children who are raped. This defies all Christian values as we know them. Further, Christian Nationalists are willing to murder others to enforce their ideals, including abortion doctors and staff.

So arguing against Christian Nationalism based on Christian beliefs seems a bit off base because the former has little to do with the latter.