My in-laws have dementia. One has Lewy Body, the other undiagnosed Alzhiemer's (she's been diagnosed with "mild dementia" but not done a follow up, and trust me, it's not mild. We've investigated the symptoms and of the common dementias the one that fits perfectly is Alzheimer's.)
If either Biden or Trump had either of these forms of dementia, their handlers wouldn't put them in front of a teleprompter or allow them to debate. FiL hallucinates frequently, and the hallucinations (and general separation from reality) often take over and cause him panic and distress (a thing called "Sundowning"),
MiL is more extreme but in another direction, she'll forget what was said to her a minute or so ago. She'll ask the same question over and over again. She'll forget things she's seen over and over again. She'll forget what she was starting to do. We find bizarre stuff happening like her putting medications in the oven or putting USB chargers in the sink. She refuses to take care of herself, not showering for days on end, avoiding personal grooming. Unlike my FiL there are no lucid periods of day, she'll have it worse sometimes than other times, but we can't bring her somewhere and ever expect her to remember how she got there, or even remember the place she went to when she goes back.
(We nonetheless got her and FiL's consent to move them from their crumbling home to assisted living, but she doesn't remember either of the two visits she made before giving that consent, let alone the consent, and occasionally gets mad at my wife over it. They need the care, and my FiL is finally being fed and showered and getting his medications, something my MiL kept forgetting to do - FiL is also unable to walk due to unrelated health problems so we had the nightmare of her being his caregiver and not doing it.)
Yes, it's as miserable as it sounds.
But, getting back on topic, moreover, the idea that Biden or Trump have either of these conditions is laughable. How do you put someone in front of a teleprompter who will literally forget why he's in front of a teleprompter? Or if he hallucinates giving his speech, how do you deal with this? Can you imagine either politician suddenly panicking in the middle of a speech because they don't know why they're there or they think it's a fake event?
And what's the evidence either do have it? What prompted these armchair diagnoses?
That Trump's speeches are kind of crazy and he forgets the names of people he only occasionally deals with? If the latter is a sign, then I've had dementia since I was in kindergarten (or UK equivalent, Class 1 ;-)) As for the former, yes, he's probably running out of steam (so, good job we're moving away from steam power to electric boats huh? That was a joke.) But he ultimately is an improvisor, he hates reading prepared speeches, and he's tired, worn down, and clearly miserable. His capacity for coming up with material for his speeches is at a low, but one can assume this is more about running out of steam than neurons.
Biden has had a stutter that he's had to overcome since he started in politics which is why he's famous for his "gaffes". Most of the recent examples highlighted by the media and "OMG DEMENTIA" critics are no different to what he was doing 10, 20, even 30 years ago. The only recent sign of mental deterioration anyone's been able to come up with was that mumbling performance at the debate. But mumbling is... mumbling. A physical, not mental symptom of something. Reading the debate transcript it's clear Biden was speaking clearly and mostly in as complete sentences as you'd expect anyone to in an unscripted debate. He's understanding the assertions made by Trump and giving coherent on-topic responses. His thought processes are not perfect, but they're not unusual or unexpected in an otherwise healthy person.
At worst, mumbling suggests Biden is physically not mentally deteriorating. He's literally lacking the energy to speak up in the booming voice people expect from politicians.
I am not a doctor or neurologist. It is entirely possible that there is some form of dementia that fits Trump and another that fits Biden, but the reality is I'm finding that hard to believe. The reality is that all forms of dementia end up addressing issues that at least overlap with the two forms I am painfully familiar with, and I just don't see the evidence with either politician.
This is an invented issue. The New York Times has taken the Trump's smear campaign against Biden (which itself may have either been prompted by, or prompted, the suggestions Trump has similar issues), treated it as real, and turned it into a campaign to get rid of a very effective liberal politician.
Here's the debate transcript, read it for yourself. And bear in mind all of these are off-the-cuff answers to often unexpected (Trump was inventing shit over and over again) assertions, so yes, some stumbling over words is to be expected especially from someone with a stutter, but ask yourself if Biden ever went off-topic, forgot what was just said, or came up with word salads.
https://www.cnn.com/2024/06/27/politics/read-biden-trump-debate-rush-transcript/index.html
Please vote for the guy with the stutter, and against the fascist, 'cos the guy with the stutter (1) isn't a fascist and (2) is actually trying to make everyone's lives better, even if he doesn't see eye to eye with you on everything.