see 61
And I would argue that Congress is empowered to determine what citizenship is. And their determination, based on the definition prevailing between 1952 and 1986, makes Ted Cruz -- born of a Cuban father (but a legal resident of the USA) and an American mother who met the requirement of living in the USA a total of ten years, at least five of them after the age of 19 -- a citizen at birth as opposed to a naturalized citizen. There being no classification called "natural born citizen" in U.S. law, Cruz is thereby eligible to serve as President.
More importantly, recognize that this opinion is shared by almost all of the relevant experts in the country. The opposing view is not.
In Cruz's case, the birthers are tilting at windmills.