You will note that the qualification to be a Representative or Senator is simply "citizen," but the qualification to be President is "natural-born citizen."
Question: Why add the extra criterion if there are only two classifications for citizen?
Answer: Because "natural-born" is not a classification of "citizen," it is an extra qualification to be met for the citizens who wish to become President.
The Preamble of the Constitution says "We the People of the United States, in Order to... secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America."
There is your constitutional definition of natural-born citizen right there at the beginning of the Constitution: "...ourselves [We the People] and our Posterity [future children]."
Natural born citizens are the children born of We the People, for whom the Constitution was ordained and established to secure. How else would they "secure the Blessings of Liberty" except by limiting the qualification for the highest office in the land to the citizen children of citizen parents?
-PJ
I believe, and this is just my interpretation, that a NBC is either born in the United States to a parent who is legally there, or a baby born an automatic American anywhere in the world.
Thus John McCain did not need his congressional ruling to be a NBC. Born to two American parents serving their country (well, mom was accompanying her husband). No question.
Thus if Obama was born outside this country he would not be a NBC or even a citizen at birth and would have needed naturalization because the only parent with citizenship was not old enough to confer it.
Thus Ted Cruz would be a NBC because he was automatically American at birth.
Thus a Schwarzenegger would not be, as he was born outside the country to two non citizens.
I think my interpretation is the fairest. Naturally Born American. The second you are born, you are an American. I add the disqualifier that keeps anchor babies from that status.