8 USC § 1408The following shall be nationals and citizens of the United States at birth:
(g) 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 person, was physically present in the United States or its outlying possessions for a period or periods totaling not less than five years, at least two 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, or periods of employment with the United States Government or with an international organization as that term is defined in section 288 of title 22 by such citizen parent, or any periods during which such citizen parent is physically present abroad as the dependent unmarried son or daughter and a member of the household of a person
The law applicable at an other time
The Naturalization Act of 1790Be it enacted by the Senate and House of Representatives of the United States of America, in Congress assembled, That any Alien being a free white person, who shall have resided within the limits and under the jurisdiction of the United States for the term of two years, may be admitted to become a citizen thereof on application to any common law Court of record in any one of the States wherein he shall have resided for the term of one year at least, and making proof to the satisfaction of such Court that he is a person of good character, and taking the oath or affirmation prescribed by law to support the Constitution of the United States, which Oath or Affirmation such Court shall administer, and the Clerk of such Court shall record such Application, and the proceedings thereon; and thereupon such person shall be considered as a Citizen of the United States. And the children of such person so naturalized, dwelling within the United States, being under the age of twenty one years at the time of such naturalization, shall also be considered as citizens of the United States. And the children of citizens of the United States that may be born beyond Sea, or out of the limits of the United States, shall be considered as natural born Citizens: Provided, that the right of citizenship shall not descend to persons whose fathers have never been resident in the United States: Provided also, that no person heretofore proscribed by any States, shall be admitted a citizen as aforesaid, except by an Act of the Legislature of the State in which such person was proscribed.
Had Congress so chosen the laws codified as 8 USC § 1408 would have provision to declare certain persons "natural born citizen", just as Congress has chosen at other times. Congress made no such provision and the law does not have such provision.
The law (8 USC § 1408) states that Cruz is a citizen.