He has a Glioblastoma brain cancer. My brother-in-law had that and there is no cure. He will start talking all crazy. Even though they said they removed McCains, it probably just made it spread faster.
That's always the case. Surgery to remove it tends to make things worse.
The part of the brain that is impacted by the brain tumor determines which functions of the body are effected. My sister died from this. It is a horrible diagnosis. Her speech was not changed, but motor skills and various types of thinking were.