The word “dementia” is being tossed about here with little regard to what it actually means. It is a word that has a specific technical meaning and is not something that can be diagnosed by simply watching someone on TV or reading their tweets. There is no specific, single identifying symptom of dementia. Statements someone doesn’t like, decisions someone thinks are bad, slips of the tongue, lapses of memory, spelling or grammatical errors, calling another national leader “Rocket Man” and comparing your button to his, cutting off aid to Pakistan, enforcing the law as written, not believing in global warming, referring to yourself as a stable genius, acting like an idiot at times, doing inexplicable things, being unethical, etc. are not specific symptoms of dementia. Taken all together they do not make the diagnosis of dementia. To make a diagnosis in this manner is no more valid than diagnosing Hillary as having seizures based on a few movements seen on video.
Dementia is a syndrome, a group of symptoms that occur together, not a specific disease. There are many diseases that may result in dementia such as Alzheimer’s disease, Lewy body disease, and vascular disease to name only a few. The DSM V actually eliminated the term “dementia” and replaced it with the term “major neurocognitive disorder” but the diagnostic criteria are essentially unchanged and they are (taken from the DSM V):
Evidence of significant cognitive decline from a previous level of performance in one or more cognitive domains (complex attention, executive function, learning and memory, language, perceptual-motor, or social cognition) based on:
Concern of the individual, a knowledgeable informant, or the clinician that there has been a significant decline in cognitive function; and
A substantial impairment in cognitive performance, preferably documented by standardized neuropsychological testing or, in its absence, another quantified clinical assessment.
The cognitive deficits interfere with independence in everyday activities (i.e., at a minimum, requiring assistance with complex instrumental activities of daily living such as paying bills or managing medications).
There are a couple of other technical requirements that are not pertinent to this discussion.
As you can see the first criteria requires a “significant cognitive decline” in one or more areas of functioning. I don’t believe anyone can give specific examples from available sources to conclusively show there has been a significant decline. I don’t think there is any available evidence that even strongly suggests there has been a significant decline.
Has Trump himself, a knowledgeable informant (not an anonymous source), or a clinician who has actually examined him expressed concern that he has experienced a significant cognitive decline? Both Theresa May and Mike Pompeo, though not clinicians, have at least interacted with him in circumstances that would be likely to reveal significant cognitive impairment, and they say no. Has there been standardized testing or other quantified clinical assessment? If there is, it certainly isn’t public knowledge. Does he require assistance with taking his medications and paying his bills? I don’t know but I rather doubt it.
For anyone other than a qualified professional who has actually examined him to diagnose that he is demented is simply name calling and should be given the weight it deserves. Absolutely none. Now if you want to call him demented, a moron, an idiot, or anything else in the slang rather than technical sense of those terms, have at it, but don’t then try to pretend that you made a real diagnosis carrying any weight or satisfying the requirements of the 25th Amendment.