There is a strong argument based on the case of Wong Kim Ark v. U.S. that Cruz is not a "natural born citizen" because he was born outside of the U.S. and inside of another country (and his parents weren't part of the U.S. diplomatic mission to that country). That position is not a foregone conclusion based on that case because the case itself dealt with the application of the 14th Amendment to the child of Chinese subjects who at the time of his birth were domiciled in the U.S. in the course of discussion, however, the Court went over the history of citizenship and alienage by birth, noted that the clear common law rule had always been that an individual was a citizen of the country where he was born, even if his parents were not, and held that the 14th Amendment essentially restated the rule as it had always applied to whites and then made that rule's applicstion to everyone mandatory, regardless of race. In other words, the 14th essentially restated the ancient rule that citizenship in the place of birth arose automatically (i.e., "naturally"). The two basic exceptions being for children whose parents were part of a diplomatic mission or an occupying foreign army.
As I said, Cruz' case is the opposite of the facts dealt with in Wong Kim Ark, but the case did rest on what was considered normative common law at the time and therefore is strong persuasive authority for the argument that Cruz is not a "natural born citizen".
Too bad, because look at the white trash "natural born citizen" we have in office now; NBC doesn't provide any guarantee of value.