I don't see any evidence of dementia. He's just visibly slowing in front of us, just like Biden did.
The difference is that, with the slowing, he's becoming even nastier, more miserable, more needy, more aggressive. He knows what most people think of him. It's like he's just given up and said, "**** it, I'm just gonna make you all pay".
That's dangerous as hell, and it was already dangerous enough. No doubt there is a lot of concern in the people closest to him, but as with all of his enablers, this is their fault.