I think the most relevant thing posed here in contrast to the "cognitive decline" issue is "Whether Trump is mentally ill, or severely and dangerously disordered -- a Malignant Narcissist."
But when I voted on my mail-in here in CA, I had choices of Bernie, Biden and Bloomberg. Bernie could be judged as showing his age, because he's become an inflexible ideologue seeking disruptive utopian solutions. Biden had inspired me months ago when he was in Michigan and it was one of his better days, but the debate performances caused me concern because -- daily -- I'm witness to my 95-year-old Moms and her cognitive decline. I wondered "What will Joe seem like in three years?" All three of those old fellows are about the same age, or the late 70s. -- either 77 (Biden) or 78 for the other two.
Bloomberg seems to be holding up better than the other two. Even so, as if he were standing down some badass in "High Noon", I wish he had been quicker to bow out and before the CA primary, rather than after it. And I say that even in spite of the vote I gave him on my mail-in.
It's the Smorgasbord Myth that defeats us in contrast to a Unified War Strategy. We want a little of this, a little of that -- "I'm a voter and I deserve a smorgasbord because this is 'Murica'!" Think about it: that's the force that catapulted Trump. "You mean, all we have as a sane choice is HILL-ARY?! Screw that! I'm voting for the Asshole! If I can't have my smorgasbord, F*** everybody and everything !"