Some debate exists as to the meaning of this phrase. Consensus exists that anyone born on U.S. soil is a "natural born Citizen." One may also be a "natural born Citizen" if, despite a birth on foreign soil, U.S. citizenship immediately passes from the person's parents."
Such restrictive term exists in the US constitution. Aside from the other constitutional requirements, a person running for the Presidency or the Vice presidency should also be a "natural born" citizen. In an article written by Neal Katyal and Paul Clement, "On the meaning of natural born citizen," published at the Harvard Law Review Forum, we learned that the phrase was included by the founding fathers of the US constitution to discourage foreigners from entertaining thoughts of running for the presidential post:
As recounted by Justice Joseph Story in his famous Commentaries on the Constitution, the purpose of the natural born Citizen clause was thus to “cut off all chances for ambitious foreigners, who might otherwise be intriguing for the office; and interpose a barrier against those corrupt interferences of foreign governments in executive elections.”
In many instances, the US considers anyone born within their jurisdiction as "natural-born" following the principle of jus soli. However, the US also considers those born of American parents abroad as still natural born, following the bloodline of the parents, hence adhering to the principle of jus sanguinis.
Black's Law Dictionary (9th Edition) defines "Natural Born Citizen" as "A person born within the jurisdiction of a national government." Since our jurisdiction follows the US, we may definitely say that the status of being "natural born" is granted to those persons who do not need to do anything or do not need to go thru a process before assuming or attaining citizenship.
Now, let me say that the phrase "natural born" does not connote citizenship--it connotes a status. In jurisdictions where the jus sanguinis principle is respected and recognized, it follows that to be "natural-born", one needs to have parents with at least one of them, a Filipino citizen.
In the case of Poe, it is clearly uncertain if she had Filipino parents, therefore, the "natural-born" status cannot be ascribed to her, because, again, our jurisdiction clearly follows the jus sanguinis principle. Meaning, she may have been born here, but statutes do not automatically grants her the status of "natural born" being silent as to the real citizenship of her parents.
So, then, if we now recognize Grace Poe as a Filipino citizen, yet, not natural-born, does it follow that there are citizens right now who are not natural-born? Yes, those who need to do or to undergo a process before they are granted a status, and that status is what we call "naturalized".
Hence, in the case of Grace Poe-Llamanzares, she was born here but since the citizenship of her parents were unknown, she becomes a Filipino citizen but not natural born. When her birth certificate was accomplished, meaning the foundling certificate, Grace automatically by virtue of adoption and thru a court proceeding, became a naturalized Filipino citizen.
Now, here comes the complication.
Poe-Llamanzares went to the states and got married. She was then recommended by her natural-born American husband for naturalisation. The US government eventually granted her such shortly after she swore allegiance to the American flag. What she lost was not her being "natural-born", but her status as a Filipino citizen of "not natural born".
When she became a US citizen, Grace Poe-Llamanzares altogether lost all Filipino citizenship. She is not a citizen anymore of the Philippines, but of the US. SO, this is not a simple case of someone losing her being a "natural-born" Filipino citizen, oh no. This is a principle of allegiance already, which means someone's fidelity or fealty to a country, a nation.
This, then becomes, from a question of fact, to a question of law, and not just a legal question but possibly a justiciable political question, something I fear would not be resolved by just a mere decision by the Supreme Court, and the Court can even say that it is not within their jurisdiction to solve a purely justiciable political question.