I am convinced he was born a dummy.
His school records support that theory.
Look at the 1987 video from CSPAN of him campaigning in New Hampshire when he confronts an audience member who asked him a challenging question on a particular policy issue. Biden points his finger at the guy and reels off 4-5 complete fabrications about his class standing, his supposed selection for law review, the number of credits he earned, his IQ (relative to the questioner) and scholarships he claimed to have been awarded.
Every one of those factual claims was false.
But if you look at the structure of his argument it could be boiled down to - I am better than you are, therefore I win the argument. The quintessence of arrogance. And then it's built on entirely false predicates!
I watched that video as it was first cablecast on CSPAN in early 1988. My thoughts at the time were - I have just seen the end of Joe Biden's political career. Was I wrong. His 1988 Presidential primary candidacy was indeed over (shortly after 60 Minutes ran their piece on the Kinnock speech.) He just kept on ticking.