Different mental health professionals have different theories, but Dr. Jerrold Post (psychiatrist and CIA political profiler, author of "Dangerous Charisma" argues both Trump and his followers are damaged, but in different ways, not in like ways. The followers are damaged in a way that makes them crave an authoritarian "father" figure who can make their psychic distress go away, usually by promising to alleviate real world "problems" that they mistakenly believe are the cause of their distress.
"The Dangerous Case of Donald Trump" contains many essays that basically say Trump was damaged very early. He could not tolerate the emotion of shame so he produced an arsenal of defense mechanisms that shield him from the truth and lead him to crave approval. His followers provide exactly the narcissistic fuel he requires to maintain his fantasies of unlimited success
Both of those books are quite extraordinarily, but IMO "Dangerous Case" covers far more ground and is the better of the two books.
PS: I don't know if either Trump or his supporters have enough insight to "hate themselves." I know Trump could never admit that to himself. Their grievances are external, but of course they are diversions from immense internal anxiety they cannot face.