Article II, section 1 of the Constitution provides that “No Person except a natural born Citizen . . . shall be eligible to the Office of President . . . .” A person must be a citizen at birth to be a natural born citizen. Senator McCain was born in the Canal Zone in 1936. Although he is now a U.S. citizen, the law in effect in 1936 did not grant him citizenship at birth. Because he was not born a citizen, he is not eligible to the office of president.
Why Senator John McCain Cannot be President: Eleven Months and a Hundred Yards Short of Citizenship,
Mich. L. Rev. First Impressions
Available at: https://repository.law.umich.edu/mlr_fi/vol107/iss1/23