The problem, of course, is that you're conflating half a dozen different things, domestic and foreign, while also trying to neatly separate them (in a way that makes sense for you). It, uh, doesn't actually work like that in practice? And I feel like that's what a large part of the disconnect is.
While what we're currently describing as Christian Nationalism is aptly summarized as such, it's not a new concept by any means. And when you look at the people pushing back at it, there are minimally two large camps: Something akin to anti-Fascists, of any stripe, that see the movement as the authoritarian and anti-democratic power trip that it is. But also a different
style of Christian Nationalist, that don't disagree with the messaging as much as they do
the way that message is being presented.
There is no separating American dominance/excellence/similar concepts and religion. They're the same thing. And, by and large, the people in power - the ones that aren't just blatantly in it for power and influence (and by extension, money) like Trump -
do care about religion. Their personal religion, that does not necessarily strictly adhere to your interpretation nor the "actual" words and teachings. Y'know what I mean?