This was brought up on a local radio show about a month ago. Here's waht I found back then. Doesn't seem to be an issue for McCain.
http://en.wikipedia.org/wiki/US_citizen#Through_birth_abroad_to_two_United_States_citizensBirth within the United States
Main article: Birthright citizenship in the United States of America
Children born in the United States (including not only the 50 states and the District of Columbia, but also, in most cases, U.S. Territories, such as Puerto Rico, Guam, the Northern Mariana Islands, the U.S. Virgin Islands, in addition to many current states which were territories at the time of the birth of some individuals now living, e.g. Alaska and Hawaii), are U.S. citizens at birth (unless born to foreign diplomatic staff), regardless of the citizenship or nationality of the parents (see Jus soli). This has become controversial, as some non-resident parents, especially undocumented immigrants, enter the United States to give birth, so that their children, often called anchor babies, will be U.S. citizens. A birth certificate is considered evidence of citizenship. This differs from most western nations; countries of the European Union which awarded citizenship to children born there (such as Ireland) closed this possibility.
The U.S. citizenship status of children born in the United States to non-citizen parents has been generally accepted as settled law since 1898, when the Supreme Court held in U.S. v. Wong Kim Ark that almost all such children were entitled to citizenship by the Fourteenth Amendment to the Constitution. Although efforts have been made in Congress, from time to time, to overturn the Wong Kim Ark ruling or limit its effect, via either a new amendment to the Constitution or ordinary legislation, no such attempt has ever succeeded.
[edit]Through birth abroad to two United States citizens
See also: jus sanguinis
In most cases, one is a U.S. citizen if both of the following are true:
Both parents were U.S. citizens at the time of the child's birth
At least one parent lived in the United States prior to the child's birth.
A person's record of birth abroad, if registered with a U.S. consulate or embassy, is proof of his or her citizenship. He or she may also apply for a passport or a Certificate of Citizenship to have his or her citizenship recognized.
