One of the main reasons for antagonistic narcissism is childhood trauma, such as neglect, emotional abuse, or inconsistent caregiving. These early experiences can lead to deep feelings of insecurity and a heightened need to protect themselves by putting others down.
This will help to explain Its an article from People magazine that provides an excellent overview of what shaped Trump's fatally flawed personality. From the best selling book Too Much and Never Enough Mary Trump's book.
"Mary writes: "Donald's problem was that the combative, rigid persona he developed in order to shield him from the terror of his early abandonment, along with his having been made to witness his father's abuse of Freddy, cut him off from real human connection."
From this view, Too Much and Never Enough traces the "parallel lines" of Freddy's deterioration despite his nominal place as the family scion and the rise of his younger brother Donald, here described as a brash, boundary-less bully — not so much greedy as a black hole, warping any rule or restraint around him."