He lost his balls after Madonna made a fool of him and he begged, begged, begged, to get Hillary on when she was running for Senate. He probably relied too much on his ultra-lib writers after a while, and the whole thing with Margaret Ray, his stalker, didn’t end well, so he just got to be a miserable sod after a while.
Losing out to Leno for the Tonight Show gig...that seems to have blown every circuit in his brain.