McCain is blind with Trump hate. That’s the key.l
I'm not a psychiatrist.
That said, I suspect that McCain is also settling a score with US, the voters.
After all, we chose to not elect him, and did elect Trump.
He has no idea how, in the twilight of his career, just how much better he would look if he sided with our very fine country instead of a descent into petty envy and child-like jealousy.
.
Trump has spit on a lot of people and everyone of them is looking for a chance to get even
He is blinded by Trump hatred AND ... his clock is ticking.
That hate is doing more to keep him alive than any medical procedure his doctors can administer........