I note that some people on this thread seem to be looking for signs of dementia (possibly due to Alzheimer's Disease, although there are other causes) in Trump's behaviour and outpourings. However dementia, whatever it's cause, is something that has a gradual onset.
I view it as far more likely that DT has ALWAYS had a personality disorder (i.e. from birth) but it's only now, with so much media scrutiny of the way that his mind seems to work, that it's become particularly noticeable to many people. (I suspect though that many people who've had business dealings with him in the past could also provide evidence of such a personality disorder).