My source is the holding in the Wong Kim Ark decision. The Court talks about "natural born citizen" all throughout it's dicta, but in it's holding, they simply call him "citizen."
Wong Kim Ark very explicitly refers to a case (Minor v Hapersett) finding that “natural-born citizen” means “citizen by birth” in the context of the 14th amendment, and uses that definition to base its ruling.
Dicta. They didn't put "natural born" in the holding.
Dicta is just musing and thinking out loud by the court. Only the Holding has legal relevance.
Oh come on, the holding is that ‘[t]he child born of alien parents in the United States is held to be a citizen thereof, and to be subject to duties with regard to this country which do not attach to the father.’ You can’t separate that holding from the basis of it. And in fact, there is no distinction made in the text between dicta and holding, such as in modern cases, where it separates the two by the literal word, “Held.” In fact, the dissent explicitly describes the definition as “held” by the majority (”Thus, the fourteenth amendment is held to be merely declaratory, except that it ... puts that rule beyond the control of the legislative power.”)
The dissent acknowledges the common-law definition, but merely argues that common law isn’t necessarily in effect after the passage of the Constitution, a position held by no conservative on the Court, nor to my knowledge on any appellate court, arguing “if that amendment bears the construction now put upon it, it imposed the English common-law rule on this country for the first time, and made it ‘absolute and unbending,’ just as Great Britain was being relieved from its inconveniences.” In fact, it’s the DISSENT that argues that “natural-born citizen” may be defined by statue! “Nationality is essentially a political idea, and belongs to the sphere of public law.”
In fact, the dissent shows explicitly where Vattel’s definition is in direct conflict with the 14th amendment altogether: “I say that, in order to be of the country, it is necessary that a person be born of a father who is a citizen; for, if he is born there of a foreigner, it will be only the place of his birth, and not his country.”
That’s right: if we were to adhere to Vattel’s political theory, we would find that the 14th amendment directly overturns the Constitution’s definition of “natural-born.” To be clear, the dissent wouldn’t; the dissent argues that obligations to one’s country of birth should be set by legislation. I’m using Vattel herein to make a different point than that made by the dissent. And to be clear: I don’t actually think that the 14th amendment overrides the Natural-born clause; I don’t think Vattel is relevant to U.S. law. Keep in mind that this is the DISSENT. I only reference it to show that the dissent considered Vattel’s definition utterly inconsistent with Ark. But the problem with the dissent is that not just the majority, but the 14th amendment itself is in direct contradiction to Vattel.