The original quote happened because halfway through it he realized he was about to say "shame on me"
it's pretty funny to look back on that given that today we have Trump saying just deranged shit all the time on stage with no real consequences, and Biden, who can barely go two weeks without giving a speech where he completely forgets who and where he is for a solid 15 seconds. just like the Dan Quayle potato thing. seems so quaint in retrospect.
if either of them said "shame on me" today it would be forgotten in less than an hour. screw misspelling, Biden could just say the word "potato" repeatedly while he's reminsicing about his mother's cooking in the middle of a speech announcing the beginning of WW3 and nobody would care
Agree to disagree he starts saying the second part, gets a far off stare that looks like he realized he was about to completely undercut his point and so changed the second half of the saying to the exact opposite of the actual saying, thereby further undermining himself.
Could very well be occams razor but I'm going with the funniest stupidest answer is the right one.