Start here Pub.L. 82-414 § 301(a)(7),(b); 66 Stat. 236
Section 301 (a) (7) A person born outside the geographical limits of the United States and its outlying possessions of parents one of whom is an alien, and the other a citizen of the United States who, prior to the birth of such a person, was physically present in the United States or its outlying possessions for a period or periods totaling not less than ten years, at least five of which were after attaining the age of fourteen years; Provided, that any periods of honorable service in the Armed Forces of the United States by such a citizen parent may be included in computing the physical presence requirements in this paragraph.
Okay, so this says someone in Cruz’s situation is a citizen at birth. Does mean they are not a natural born citizen.