I, like you, have the highest respect for Cruz. I have tried to stay out of this debate, because my answer to the query, being clearly ambivalent, might be taken as taking sides, as between Cruz & Trump, which is something I have decided to avoid, at this juncture. (As I have posted, we are going to need both the Cruz & Trump supporters--whose perspectives really do complement--that is to complete--each other--if we are going to turn America back towards her heritage.
But let me offer a perspective, which has clear implications as to the original intent, of the framers of the Constitution. The foremost authority--the best accepted authority--on the Law Of Nations, to the founding fathers was De Vattel. Here is his answer to the query:
It is asked whether the children born of citizens in a foreign country are citizens? The laws have decided this question in several countries, and their regulations must be followed.(...) By the law of nature alone, children follow the condition of their fathers, and enter into all their rights (Sec. 212); the place of birth produces no change in this particular, and cannot, of itself, furnish any reason for taking from a child what nature has given him; I say, "of itself," for civil or political laws may, for particular reasons, ordain otherwise. But I suppose that the father has not entirely quitted his country in order to settle elsewhere. If he has fixed his abode in a foreign country, he has become a member of another society, at least as a perpetual inhabitant; and his children will be members of it also.
I realize that given the various aspects of the Cruz case, this does not necessarily clarify all issues.
“By the law of nature alone, children follow the condition of their fathers, and enter into all their rights”
‘Following the father’ might go all the way back to Roman law. Or could it be Code Napoleon? I’m not sure when we might have expanded this to include the mother. There was some change around 1920.