kEiThZ
Superstar
How quickly we forget. There was a very fierce and almost year-long debate about McCain through 2007 and 2008. The US Senate actually went as far as to pass a resolution (sponsored by then Senators Obama and Clinton, among others) to declare John McCain was a "natural born citizen." They wouldn't be bothered to do that if "nobody questioned it." They even hinged that resolution on the fact that the US military occupied 'Canal Zone' was technically an extension of "American soil," which actually reinforces that whole requirement, strengthening it as a precedent.
A bit of primary politics is hardly that big a deal. And as you note, it was McCain's opponent who supported his claim. Very different from what we're talking about today. That affair meant Ted Cruz got a substantially easier ride.