Why a Trump-Cruz ticket could be next after South Carolina debate

Fox News ^ | January 15, 2016 | Douglas E. Schoen

[Cboldt]

-- I don't know of any country that allows one to become a citizen without first meeting the residency requirements, save a child of 2 US citizen parents who later became citizens of a foreign country while the child is a minor --

Again, careful with words. There are multiple players potentially involved in residency.

Parent needs residency in order to pass citizenship by blood.
New citizen may need to establish residency in order to get or to keep his citizenship.

If Cruz had stayed in Canada his whole life, he'd be a US citizen today.

[patlin]

I don't see it that way. Cruz would only be a US citizen today if he, at his coming of the age of consent, had NOT acted upon his Canadian citizenship so as to become a member of the Canadian political process. Again, see Perkins v. Elg, 307 U.S. 325 (1939) that covers this quite thoroughly.

[patlin]

Also ...

Citizenship at birth exists

To which I would further clarify, "the possibility of US citizenship from birth exists"