Actually, I agree that McCain is a Natural Born Citizen, but for a different reason:
At the time of McCain’s birth, McCain WAS born a U.S. Citizen.
Congress can NOT make “natural born citizen” status “retroactive” -— However Congress CAN make citizenship, SIMPLE citizenship, retroactive.
McCain’s parents, at the time of McCain’s birth, had qualified, by age and residency, to pass full Citizenship to John McCain, at birth.
To be a “Natural Born Citizen” you must show that the law in place, at the time of your birth, made you a citizen, from the moment of birth. It is just that simple.