"Natural born" is practically redundant, especially since the legal phrase predates artificial insemination by centuries. Birth refers to nativity; nativity, birth. Citizenship by descent and place of birth are equally "natural"—or should be. It is ambiguous enough that, even though both McCains parents were native to the US, and even though he was born in a US territorial possession, Congress felt obliged to pass a law formally declaring him a "natural born US citizen" prior to his '08 presidential run. Obama and Hillary were among the dozens of cosponsors; I think pretty much everyone (possibly excepting McCain) sponsored that bill.

I suspect the problem is we refer to gaining non-native citizenship as "naturalization," even though it is NOT "natural born" citizenship.