Not to pick on ScarySteve, who did some nice research, but I've had it up to here with those who mistakenly believe McCain is NOT eligible to be President. Especially those who should know better.
To put it in layman's terms: McCain is a natural born citizen by virtue of both his parents being US citizens. It doesn't matter where he was born. This is by virtue of the US Naturalization Act. It is in no way inconsistent with the Constitution of the United States, which only mentions citizenship in two places. US citizenship laws have been upheld against constitutional challenges many times (once in the very case cited by ScarySteve: the Rogers case), and have been on the books in one form or another since 1790.
For a more legalistic argument, keep reading. But I'd just like to briefly point out that the two cases sited by Steve dealt with different factual situations. Wong dealt with a child born in the US to non-citizen parents. The child was deemed a citizen via the 14th Amendments language. The other case (Rogers) dealt with a person who was born abroad who had one parent who was a US citizen. Again, a different situation than McCain. In more detail below....
The Constitution mentions citizenship exactly twice.
First. Article II, Section 1, Clause 4.
"No person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President......"
No other mention of citizenship was made in the original document. It comes up again in the 14th Amendment (in the slavery context), but that is getting ahead of ourselves.
Notice first that 2 types of citizens are eligible to be President. First, natural born citizens (whatever that is), and Citizens of the United States at the time of the Adoption of the Constitution. This is important for three reasons central to the McCain NOT eligible camp.
One, it proves that the Constitution is NOT the lone document for construing citizenship. How? At the time of the Constitution, the Founders recognized that some people who were NOT natural born citizens should still be citizens, and eligible to be President. The Constitution nowhere defines who these non-natural born citizen are? In this case, they are people who had fought in the Revolution and lived in the US for a certain number of years. From Wong at 482, CJ Fuller's dissent:
"but as men of other lands had spilled their blood in the cause of the United States, and had assisted at every stage of the formation of their institutions, on the 7th of September it was unanimously settled that foreign-born residents of fourteen years who should be citizens at the time of the formation of the constitution are eligible to the office of president.’ 2 Bancroft, Hist. U. S. Const. 192."
So, documents outside the Constitution can legally determine the rules for citizenship. This is confirmed by the plain text of the Constitution itself, which presupposes their existence and validity, and the myriad of cases that construe or interpret the law of nationality since, including the two cases cited by ScarySteve in support of the proposition that McCain is NOT eligible. And cases upholding such laws against Constitutional challenge (like Rogers, for instance). And the fact that such naturalization laws have been on the book for at least 150 years.
Two, it proves person's other than natural-born citizens are eligible to be President. By its plain terms.
Three, it mandates that outside instruments must be relied upon to define what a 'natural born citizen' is, since the Constitution does not do it. It should be noted that the Constitution does designate to Congress the power to "Establish a uniform rule of Naturalization," Article I, Section 8, clause 4. This plus the Necessary and Proper Clause and the fact teh Constitution doesn't define the term should cover any argument Congress can't pass laws on citizenship. Along with the fact that Naturalization laws have been on the books since 1790 and withstood many challenges.
Second Constitutional Appearance: Amendment XIV.
"All persons born or naturalized in the United States and subject to the jurisdiction thereof, are citizens of the United States and of the State where they reside..."
This Amendment was designed to ensure that slaves, and freed slaves were citizens of the US. By its own terms it has no impact on foreign born children of US nationals. For that, one must look to the appropriate federal law.
Again, the idea that any such federal law about citizenship would somehow be unconstitutional merely because of Amendment 14's opening sentence, or because of Article II's language is patently absurd. Laws are unconstitutional when they are in conflict with the Constitution, and any naturalization law not in such conflict is not, has not, and will not be unconstitutional.
When the Constitution is silent on a point, federal law (or state law) can flush it out. Provide the specifics. As long as it doesn't conflict. Does the 4th Amendment preclude Congress from passing laws on say, Foreign Surveillance? (FISA anyone?). Same thing with agency regulations flushing out laws. As long as there is not a conflict, they are valid.
Point being, according to the current, valid, and fully Constitutional Naturalization Act (Found it Title 8 of the US Code), McCain is a citizen, at birth, hence a natural born citizen, as opposed to a naturalized citizen. Thus, he can run for President.
Sorry for the length, I just thought the whole thing was getting a bit out of hand.