I live in AZ. I was under the impression the GOP primary was open. I seem to recall when McCain was running for Senator last time, he pressured the state party to keep the open primary. Now that the state GOP has finally censured this old fossil, I hope he decides it may not be a good idea to run again.
California has an open primary system and it's one of the things that has destroyed the Republican party there. When you allow your opponents to choose your party's candidates, you're going to loose. That's one reason why the first campaign I worked on after I moved here in 2011 was "No On 121".