His mom is a US citizen, so the place of his birth is irrelevant.
Which is why the Obummer Was Born in Kenya thing always bugged me - he still would have been a US citizen.
Apparently this is actually up for debate, because it's not quite clear that "natural-born citizen" means "citizen at birth". Some argue that it means "citizen by virtue of the rules in the constitution" (as opposed to by virtue of the rules set up by an act of Congress, which is how Cruz got his citizenship at birth).
See: http://www.bloombergview.com/articles/2016-01-12/is-cruz-natural-born-well-maybe
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