I think Trump is just an average idiot who applied for and to his own surprise, was hired to do a job he was never anywhere near close to being qualified for nor mentally or emotionally equipped to handle.
What I think what we're seeing out of him behavior-wise, is less a case of cognitive impairment brought on by dementia, as just his natural dull-witted, thick-skulled stupidity resulting in a lack of ability to fully comprehend complex issues and articulate or even form coherent thoughts on them.
IOW, he's such an incredible dumbass, he comes across as being mentally impaired.
Spot on. However, he does appear to have attention deficit problems. That’s been documented by any number of people who have dealt with him.