“McCain is not running again.”
Has he come out and announced that? I’m not 100% on board with the whole brain tumor thing. Some people will feign anything to get a pass on wrongdoing; he’s certainly not above that.
If he runs again, and he was lying about dying, then he’s vulnerable, and if anyone deserved a tough primary fight, it’s him. But if he’s dying, his named successor will have to be very unpalatable in order to be effectively primaried. Dying senior senator war “hero”es usually get their successor.