Biden's problems is that he's trying to say too much at one time. So it's hard to "understand the words that be coming out his mouth". He's probably forgotten more than Trump has ever known though.
I mean, you aren't exactly setting the bar high with that analogy, but I'd still probably disagree. Biden has always come off as a few tacos short of a taco salad, it's just getting highlighted with the extra pressure of a presidential campaign.