I've been thinking the same thing. I grew up with a nearby narcissist. Not one as bad as Trump, but I know the signs well enough.
However, the world that Trump imagines revolving around him just gets wackier and less predictable every day.
So, yeah, maybe dementia, or as I suggested yesterday, maybe he wants to be president so he can renegotiate his Chinese and Russian dealeos. That, or at least get Secret Service protection for Himself.