Doug Mataconis tackles questions on McCain's citizenship:

In it’s current form — which is set forth in Title 8, Section 1401 of the United States Code, American citizenship is defined as follows:

The following shall be nationals and citizens of the United States at birth:
(a) a person born in the United States, and subject to the jurisdiction thereof;
(…)

(c) a person born outside of the United States and its outlying possessions of parents both of whom are citizens of the United States and one of whom has had a residence in the United States or one of its outlying possessions, prior to the birth of such person;
(d) a person born outside of the United States and its outlying possessions of parents one of whom is a citizen of the United States who has been physically present in the United States or one of its outlying possessions for a continuous period of one year prior to the birth of such person, and the other of whom is a national, but not a citizen of the United States;

Now, it’s clear that Senator McCain was born outside the continental United States — but he was born to two American citizens who had lived in the United States before he was born and he was born on an American military base in the Panama Canal Zone. Which brings 8 USC 1403 into play:

(a) Any person born in the Canal Zone on or after February 26, 1904, and whether before or after the effective date of this chapter, whose father or mother or both at the time of the birth of such person was or is a citizen of the United States, is declared to be a citizen of the United States.
(b) Any person born in the Republic of Panama on or after February 26, 1904, and whether before or after the effective date of this chapter, whose father or mother or both at the time of the birth of such person was or is a citizen of the United States employed by the Government of the United States or by the Panama Railroad Company, or its successor in title, is declared to be a citizen of the United States.

This is a non-issue and anyone that says McCain isn't a citizen should be checked into a mental institution. Stop with the ultra-nationalist talking points.