Given the Constitution, the only way to decide such a question is to have an election and count the electoral votes.
Of course, McCain didn't lose on that. He lost because the Sheeple preferred the genuine article to a facsimile in name only.
As far as the law goes, the only definition of Natural Born that will fly is, entitled to be a US citizen by birth, as opposed to naturalization. It's a bright line. McCain and Obama (and Cruz, Rubio, Jindal, and Haley) qualify. Kissinger, Schwarzenegger, Granholm, etc., do not.
As soon as you need to cite 17th-century non-citizen scholars, you lose!
I believe that you may be referring to that 18th Century author of 'Law of Nations'. You know, the book which our Founding Fathers relied upon at that Constitutional Convention. The same book Washington never returned to the New York library. He used it for guidance for how to conduct himself as President.
Marco Rubio was born in Miami, Florida, May 28, 1971, to Mario Rubio and Oria Garcia, both Cuban citizens who naturalized as US citizens on Nov. 5, 1975. Relevant law May 28, 1971 is Pub. L. 82-414 § 301(a)(1). Rubio is, in law, "citizen".
Jindal
Piyush "Bobby" Jindal was born June 10, 1971 in Baton Rouge, Louisiana to Amar and Raj Jindal. Amar and Raj Jindal entered the United States Feb 1, 1971 as permanent legal residents. Bobby Jindal’s parents were not U.S. citizens when their son was born, they were both permanent legal residents at the time of his birth. Jindal’s mother became a U.S. citizen Sept. 21, 1976, and his father became a U.S. citizen on Dec. 4, 1986. Relevant law June 10, 1971 is Pub. L. 82-414 § 301(a)(1). Jindal is, in law, "citizen".
The law could have been written such that these persons were, in law, "natural born citizen" as was done in 1790. That law was repealed in 1795. They are, in law, "citizen".