IIRC, birthright citizenship isn't quite as cut and dried as it seems. My ex-spouse worked in a passport office, and there are some weird rules about things like how many years you have to have lived in the US depending on exactly where you were born and to which parents. I don't remember all of them, but it's not quite as cut-and-dried as "you're a US citizen if you were born in the US"; you also have to be subject to US jurisdiction. So if you're born in the US, but are raised entirely outside of the US, IIRC you might not be a citizen.

I don't think that birthright citizenship for the children of people not in the USA legally is as clearly established in the Constitution as some people say.