Asserting that non-fundamentalists are "illegal aliens" in their own country -- the one that our own ancestors fought, paid taxes, and worked all their lives to build; or risked everything to get to and start over in -- is a potent statement of that exact kind of purity crusade thinking. It's the same libel Nazis told the Germans about their native Jews: We are something other, something less than, something not-American (and thus potentially treasonous), and perhaps not even quite human. We are not like the good volk of the heartland; we are decadent urban intellectuals who seek to corrupt all that is good. Our very presence desecrates the pure soul of the nation. We have been ejected, in their minds, from the protection of American law and the community of American citizens.Putting aside whatever quibbles one might have about what level of alarmism is appropriate to how close or not Christian nationalists are to achieving their goal (I don't think they're close but I think they're far closer than they should be and also think that its not overt violence that we need to worry about but rather the slow and subtle erorison of democracy), the analysis that such out-group thinking is part of a foundation for totalitarian logic is dead on.
For that reason, we don't belong here; and this country does not belong to us. And, underlying it all, there's the hint of a threat that as soon as the theocrats consolidate their grip on power and finish dismantling those pesky rights (they're oh, so close now), they will be fully justified in putting us behind barbed wire, removing us from "their" country by force, or simply dispatching us on sight like the vermin we are.
And to further add to that, I'd again reiterate than in pre-Nazi Germany the idea of being a "real" German was inseparable from the notion of being a Christian German; which is part of why it was so easy for so many Germans to see Jews as "aliens" in their midst.