At the time of McCain’s birth, was the Panama Canal Zone U.S. soil?
Forget it...2 American citizen parents “trumps” anything else you might be considering.
Embassies and foreign military bases are considered US soil for purposes of law enforcement[1]. I've read that McCain was born in a military base hospital.
I think McCain is just a red herring. There's no question of what nation his loyalty is towards - his father was active military with sworn allegience to the constitution of the US. His mother was also citizen.
What kind of a loyalty is a child going to have being born of a Kenyan father and an underage mother? This is one case where you have to take into the intent of the founding fathers.
[1] That's causing a fair amount of trouble in Okinawa.