There is a growing concern that Trump is suffering from some sort of incipient dementia or neurological impairment. Last week, I read an article that reported a study of the deterioration in Trump's capacity to express himself verbally. The difference is dramatic. Of course, diagnosis would require a professional evaluation -- but it is easy, and unsettling, to observe the difference.  The article is here:
https://www.statnews.com/2017/05/23/donald-trump-speaking-style-interviews/