But what is the definition of natural born citizen?
Whatever you want it to be.
Whatever it is, Cruz clearly isn't one, and it is easy to prove. Anchor-baby Rubio isn't one but probably skates first because he's not going to get the nomination, and after that because SCOTUS screwed up the Wong Kim Ark case and it will take intense immigration pressure to revers - and our overlords think we aren't under enough immigration pressure, so they'll argue that anchor babies are entitled to NBC status.
I'll give it a shot as if the constitution was followed: person born a citizen of one of the several states of parents who do not owe an allegiance to any other country