At least Trump, for all his obvious caveats, is at least coherent and can answer a question without losing himself in a fog of confusion unlike Joe...
While I agree that Biden is definitely harming the Democratic party by staying in the race and has serious cognitive decline, I far from agree that Trump is ever coherent or can answer a question without losing himself in a fog of confusion. He trades in incomplete sentences, fractured thoughts, and buzz words. He speaks like a freshman trying to write a term paper the night before it's due. Both candidates are hot piles of shit and the US is in a genuinely scary place politically right now.
I do take some issue with people making fun of Biden for his slips. First, he has had a speech impediment his entire life that accounts for some of them. Second, any further slips he has are due to his aging, which is not something he can control. It's like making fun of someone in a wheel chair for being unable to walk. Biden's slips are, to me, sad and deserving of pity or sympathy, not ridicule.
Trump's incoherence, on the other hand, is due to his having nothing substantive to say about almost anything, and being a genuinely inarticulate person. But then again it's not like his being 78 constitutes his being a spring-chicken compared to Biden's being 81. So he's likely suffering cognitive decline as well. Still, Trump's lack of coherence seems more to me like someone who never had to put in the work to learn how to do anything properly, like write or speak. He evades questions; he doesn't answer them. And he evades them by saying random half-sentences containing superficially relevant words that provoke his audience's emotion and get them to think about something else ostensibly related but not on point (i.e., he's a red-herring addict).