Which is rather scary come to think about it.
In addition to those who are born in the United States or born outside the country to parents who were both citizens — or, interestingly, found in the United States without parents and no proof of birth elsewhere — citizenship goes to babies born to one American parent who has spent a certain number of years here.
That single-parent requirement has been amended several times, but under the law in effect between 1952 and 1986 — Cruz was born in 1970 — someone must have a citizen parent who resided in the United States for at least 10 years, including five after the age of 14, in order to be considered a natural-born citizen.