This is true. But the parents were not citizens at the time of Marco Rubio's birth. That is where the issue lies. They were here legally, they subsequently became American citizens but it is not clear that this fits with the definition of Natural Born Citizen.
As I understand it, the idea of Natural Born Citizen as a qualification for the Presidency arose out of the founding fathers fear that someone with divided loyalties (U.S. vs. England for example) could be elected President. If your parents were British citizens resident in the U.S. there would be the possibility of such a thing happening. This would have been tragic had it happened in the early years of our country, years when the possibility of the English monarchy reestablishing its rule over our 'renegade' colony were quite real.
This is not a knock on Marco Rubio. He is certainly a rising star in the GOP and he would very likely make a good President. But the issue of his eligibility is real and cannot simply be tossed aside because we all like the guy.
This issues has been discussed ad nauseam here on FR, with a few FReepers claiming that both jus sanguinis (based on the citizenship of the parents) and jus soli (based on the place of birth) are required for someone to be a natural-born citizen under Article II, section 1, clause 5 of the Constitution. However, the reality is that a “natural-born citizen” is a term used in contradistinction to “naturalized citizen,” since one refers to persons to whom citizenship was legally conferred at birth, while the other refers to persons to whom citizenship was legally conferred at some point after birth. A person who is a U.S. citizen at birth is thus a “natural-born citizen” of the U.S. An excellent academic discussion on the subject (published in 1988) may be found here: http://yalelawjournal.org/images/pdfs/pryor_note.pdf
Citizenship is conferred at birth pursuant to applicable law, and different countries have adopted jus soli, jus sanguinis, or a combination of both. In the U.S., federal law confers citizenship at birth to persons who are born (i) within U.S. territory (the 50 states, DC, Puerto Rico, U.S. Virgin Islands, Guam and Northern Mariana Islands) but only if not the child of a foreign diplomat, or (ii) outside of U.S. territory if one of both parents are U.S. citizens but with certain U.S. residency requirements for the citizen parent(s). So the U.s. has adopted both jus sanguinis and jus soli, and our jus sanguinis has a residency component for the parents, while our jus soli does consider whether the parents are foreign diplomats. Either way, if one is a U.S. citizen at birth, one is, by definition, a natural-born citizen, not a naturalized citizen.
It is a red herring to claim that persons who are U.S. citizens at birth but who may also be eligible for some other country’s citizenship should not be considered natural-born citizens due to “dual allegiances” or something. My mother was born a Cuban citizen in Havana, Cuba, and although she is a naturalized U.S. citizen (and became one before I was born, not that it matters, since I was born in U.S. soil), Castro’s Cuba does not recognize that she renounced her Cuban citizenship upon becoming an American. And there are plenty of coutries with crazy citizenship laws that would make many Americans eligible to claim birthright citizenship from such country. In fact, Germany confers German citizenship to the grandchilren of Germans irrespective of where they were born or of the citizenship of the parents, so a child born in Iowa to parents born in Kansas may be eligible for German citizenship. However, it is irrelevant what the laws of a foreign country say, because according to U.S. law that child is a U.S. citizen. People who insist that—despite U.S. law being very clear in conferring U.S. citizenship to children born in the U.S. to parents who aren’t foreign diplomats—only children born to two U.S.-citizen parents qualify as natural-born citizens are permitting foreign countries to decide what the scope of U.S. law should be. Thus, when Chester Arthur was born in Vermont, he was a U.S. citizen at birth despite the fact that he could have been deemed a British subject under British law because his father was a British subject (and, like Marco Rubio’s parents, did not become a naturalized U.S. citizen until years after his son was born); James Buchanan, Woodrow Wilson and Herbert Hoover also had one parent who was born a British subject, and U.S. treatment as natural-born citizens should not depend on whether the UK considered the child to be a British subject at birth. The constitutional requirement that the president be a natural-born citizen presupposed that the U.S. Congress, not some foreign legislature, would legislate who should be considered U.S. citizens at birth.
And the same goes for a child of Americans that is born abroad. If the U.S. citizen parent(s) meet(s) the U.S. residency requirements set forth in U.S. law, their children born abroad are U.S. citizens at birth irrespective of what the foreign country’s laws say. John McCain was born in a hospital in Colón, Panama (which lay just outside the U.S. jurisdiction of the Panama Canal Zone where his father was stationed), and Panama law would consider him to be a Panamanian citizen, but U.S. law deems McCain, the child of two Americans, to be a U.S. citizen at birth, and that’s that.
So Marco Rubio and Bobby Jindal are natural-born citizens eligible to become president, as is John McCain. And if Barack Obama was indeed born in Hawaii (as indicated by the birth certificate he provided, whose authenticity I’ll leave to others to discuss), then he’s a natural-born citizen as well, despite his father never having become a U.S. citizen. There’s a reason why those who disputed Obama’s constitutional qualifications were known as “Birthers”: he is the only president other than Chester Arthur whose qualifications as president hinged upon being born in the U.S. (While Obama’s mother was a U.S. citizen, she was only 18 years old when Obama was born, so she had not resided in the U.S. for at least 5 years after turning 14 when he was born (one of the legal requirements for citizenship at birth for babies born abroad before 1986 with one U.S. citizen parent); if Obama was born outside of U.S. territory, he would not have been a U.S. citizen at birth, and thus not a natural-born citizen.