If you read up on McCain, he's conservative, no doubt, and loves the Republican Party.

This is him trying to differentiate the GOP from Trumpism, and to settle or marginalize the far right, at a time when it is critical to do so for the health (literal and figurative) of the country.

A GOP Icon, once its nominee for President, who COULD fade quietly with his GOP Icon status intact (like, for instance, Orin Hatch is ultimately doing, and that utter wimp McConnell is refining into a political doctrine).

McCain has NOTHING to gain personally, and, in fact, may knowingly be committing his last days to the indignity of being bullied by Trump on twitter.  

Most would try to avoid that.  Hang with the spouse, tell the last bits of wisdom to the kids.  Hug the grandchildren to the point they're late for school.

Instead, he's manning up.  Big time.  

We should all be as courageous and selfless.  It's how true American heroes are supposed to be.