The psychopathy of the "base"
According to Wikipedia, "Psychopathy is traditionally a personality disorder characterized by persistent antisocial behavior, impaired empathy and remorse, and bold, disinhibited, and egotistical traits."
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They are known to wear T-shirts that say "Make Liberals Cry Again in 2020 - Vote Trump". That attitude alone explains a lot about the Trump "base".
Indeed they do exhibit anti-social behavior and show little empathy for the victims in our society. They tend to believe that their side is a huge majority, when, by all counts and polls, they are a minority in our country.
They are revengeful in nature and seldom think of the country as a whole, but rather, as different tribes where the one with the most guns and power wins the argument.
They are incapable of feeling for their fellow man and cannot fathom walking in another's shoes.
I am very inclined to believe that it is a mental illness.