Donald Trump is not mentally stable. He tweets comments uncontrollably, lies with little sense of what the truth really is. At times he behaves much like a sociopath and indulges in conspiracy theories. Many psychologists have stated that he has some form of mental illness. It's unfortunate he fooled so many into becoming our next president.
Donald Trump is a pathological liar who cares about no one but himself. The fact that he is so brazen to tell these lies without fear of the repurcussions leads me to believe that he does indeed have some type of mental disorder. Normal people do not behave that way. In addition, his temperament also seems a bit abnormal. He wastes no time in bad mouthing and complaining about anyone who dares talk badly about him. He just simply does not behave in a way typical of an adult with normal mental health status.
It would seem that Donald Trump has a mental disorder. An outsider, especially untrained in mental disorders, could never truly judge. And one would have to account for how things are presented by the media and how much of a persona Trump has created apart from his own personality. But his ability to lie and act so boldly would lead one to worry about his mental stability.
Trump has a hard time controlling his impulses. When he wants to say something, he says it. When he wants to do something, he does it. There are a lot of people that are the same way. That is not a mental disorder, it is just a personal characteristic. It's just the way he is.