>> born to us citizens is natural-born. <<
No. Its “jure sanguinis.” Natural born is “jure solis.” People born in America but living oversees are Americans or not based on their actions: If they renounced their citizenship, the fact that they were born in America is meaningless to their status as to whether they are Americans. Thus, it is only because the parents have not renounced citizenship that the children are Americans; they are Americans through their blood-relationship to Americans. In contrast, those born in America are Americans because it is the country of their own birth; it is “natural” that they are Americans, not through legal recognition of their parents’ status.
Fortunately, for McCain, 8 USC 1403 recognizes Zonians as Americans by birth (although that is subject to interpretation since it does not use the term “naturalized,” “natural,” “jure solis,” “jure sanguinis,” or any other term which would clarify by which means Zonians are Americans).
Jure solis is only relevant if the parents are not US citizens. Otherwise jure sanguinis is natural-born as established in section 1401.