The word "evil" may be tainted by its dubious theological connotations. I'd say that evil is real, though, and its wholly natural basis is in just an antisocial personality disorder such as psychopathy or narcissism.

We predict behaviour by modeling the patterns. Calling Trump "mentally disordered" or "narcissistic" is just to assign a label to the model that predicts Trump's behaviour.

I'm not saying his critics should let Trump get away with anything. I'm just saying it's unseemly to demonize someone who probably suffers from a mental illness. His illness is so bad that it deserves to be condemned. But all illnesses have a tragic aspect, too, which should be noted alongside our condemnations of Trump's inhuman conduct.