“John McCain had no eligibility issues”
You might want to (re)Google cause you would be wrong.
He's not wrong, although McCain was born in the Panama Canal zone, according to the local paper at the time.
But in reality that didn't matter. He was born "in the armies of the country" of two citizen parents. While being born born on a military base does not count as "born in the US", being born outside the country while a parent is "in the service of the country (including diplomatic service) does make them reputed, "born in the country" for purposes of the NBC definition. This is only common sense, but it is also part of the "natural law" as documented by Vattel in "Law of Nations", specifically Book I, section 217. Section 212 defines NBC, as born in the country of parents who are citizens. If one is to accept the definition, it only seems reasonable to accept the exception or clarification in the very same document, just a few short sections later.