I actually happened to talk to a neurologist about this today and they didn't buy Biden as having Parkinson's (apparently his gait doesn't match, gait analysis being a key diagnostic indicator of many neurological conditions). They're also a major lib, so it could be pure cope, but it sounded like a straightforward medical assessment to me and they're not the type to bullshit me. And for what it's worth, I just checked and even the doctor they had on Fox News said the same (he speculated it might be vascular dementia).

I don't think the specific medical diagnosis matters that much, though. It doesn't take a neurologist to see that Biden's not playing with a full deck of cards, and he's clearly getting worse and not better. And obviously his camp is never going to release results of a cognitive evaluation because it would mean they could no longer lie through their teeth about his fitness for office.