Peanut's Lucy provided inexpensive psychiatric advice.
I believe she would find that Donald has a great many repressed memories of abuse from his KKK father. His older brother did not repress many of the same abuses and sought alcohol to help repress them.

For Donald, those repressed memories of the abuse and other people's reaction to the hate he was taught created a reservoir of a need for retribution. His life's foundation is built upon sand that makes this late regressive time of his life collapse into an abyss of hate and revenge.