A recent post by a psychiatrist (from another site) comments on just that:

"...Donald Trump suffers from severe psychopathology, specifically severe narcissistic personality disorder. This is a man for whom the psychic distress caused by feeling in anyway inadequate, less than, or even second best is so profound as to lead him, on a moment by moment basis, to create his own reality to live in in which he is the Best There Ever Was.
Most misinterpret Trump's braggadocio as showmanship. It's not. His hyperbole is for him; he can't tolerate the prospect of even the slightest admission of a personal deficiency or area for improvement.
Lastly, with respect to his inability to project empathy, it's far more likely that he is incapable of actually feeling empathy. Inability to feel true empathy is often seen in those with severe Cluster B personality pathology.
... he is incapable of appreciating the emotional perspective of anyone else."