shirts for no reason when his dementia started to take hold

Possibly Trump was known for hand-shredding papers when he was younger, but I honestly don't recall any mention of it -- in fact the only such mention was when he had his staff deliberately shredding documents that could be used as evidence against him, using shredders then. Nothing at all about him shredding papers by hand. The fact he's doing that sort of thing now is, I'd guess, at least partly an expression of his frustration at being unable to understand a lot of what was written in those papers.

Throwing torn paper on the floor?

Heck, yeah, get your manhood from making other people work.
He's trash.

but honestly it is utterly irrelevant what the root cause of his behavior is -- because his behavior now isn't outside of the range of his prior behavior, only the context is different.

Trump has ALWAYS been unqualified and inappropriate for the office he now occupies, based upon DECADES of evidence in the form of words and deeds. I see no reason to ascribe his behavior in the 70s, 80s, 90s, 00s to dementia yet even then he was acting in such a fashion that he never should have so much as sniffed the Oval Office. His bad behavior now is totally consistent with who he's always been. And it is also consistent with declining mental faculties. Why give him the credit/benefit of the doubt that it is new/different/evidence of decline? I see no reason to be that charitable.

Talking about his behavior now as if it is something newly emergent, as opposed to something which has ALWAYS been, only serves to give cover to the sh*tstains who endorsed and voted for him and support him even today. It gives them a chance to claim "oh, oh... um, well *now* I see that he is deteriorating, yes, but that diminished person isn't who I voted for/supported, so what he's doing now isn't my fault."

How about this?

against him now and then just keep adding the add'l criminal counts on, since they are popping up everywhere.

Other things, such as impeachment (when Congress gets its act together) can proceed as well too, and
and of course the best thing is GOTV in 2018 and send a strong strong msg. to him and his cronies and start implementing protection measures for Mueller as well as other areas.