I believe Biden at 80 (currently) will be affected more as even his own base has admitted concern with his age and declining mental capacity. Although Trump is no spring chicken at 76yrs of age, we do not hear much concern from the Republicans about his age.
I actually think Trump is sharper than most people give him credit for. While I do think it likely he's being medicated for one or more conditions that could impact his overall mental function, I think said treatment has been working. People mistake the megalomania and flaws in Donald's character for broader dysfunction.
He's not stupid, he's just ignorant because he doesn't care about anything except himself. It's not that he cannot track details or correctly recall events, he just has no interest in doing so, and never faces consequences for blatant lies.
He's perfectly capable of following normal reasoning, but ignores it because it doesn't give him the outcomes he wants. I suspect he can even speak like a normal human being, but his "unique style" makes him and his audience feel good, so he doesn't put forth the effort to communicate more clearly.
Other than being 76 and having megalomania/narcissistic personality disorder, his brain works fine. He's just been coddled and privileged almost his entire life, and is intellectually incredibly lazy while being utterly amoral.
Unfortunately we are in very desperate times as it appears we will have to choose between these two Again. One can only hope a good 3rd party candidate will come out of nowhere and surprise us - a 1 in a Billion chance
