Trump's skillset is that of a reality TV star. He knows what to say and how to say it to engage people in drama. His presidency has been a continuation of this. It freaks out the intelligentsia because it seems insane to them that a person in such a high place of power could get involved in things like Twitter flame wars. That's low class/blue collar behavior that is totally foreign to their own culture. That is why people on the blue collar end of the spectrum are more capable of realizing that this particular aspect of his behavior does not represent a genuine threat, because it's part of their culture.
Your depiction of Trump as unstable is exactly this cultural bias I'm referring to. He doesn't exhibit the upper class white culture behaviors you're willing to accept in a president, so he seems unstable.
It's worth mentioning that while he's always been rich, Trump spent a significant portion of his youth around construction sites, so he has adopted a lot of low class blue collar behavior.
