Although I agree with your second sentence, suffice to say that attempts to rationally connect the dots between Mr. Trump and anything like “white nationalism” always seems to skip a few dots.
At any rate, the larger question regarding birthright citizenship is a rather simple one. It reads like this:
Is birthright citizenship a good national policy or a bad national policy?
That question can be debated without any allusion to race whatsoever, and in fact HAS been debated without allusion to race in the past, and both positions have been held, at different times, by liberals and conservatives.
That is fact, and in that it is fact, it throws a rather large amount of doubt on anyone who today insists that the only reason a person would oppose birthright citizenship is racism.
Hope that helps.