Trump has been described as many things- Sociopath, Psychopath, etc. One description that I have not heard is just plain old Sadist. He really does not care who he hurts at any given time, but he feels a deep need to simply hurt SOMEONE at all times.
When he is not hurting individual reporters, he hurts individual union bosses. When he is not hurting union bosses, he feels a need to hurt individual politicians who get in his way. He is constantly hurting specific individuals. Megan Kelley was just another victim from his sadism, but now he has grown bored with her and felt the need to move on to his next victim. His enablers are also sadists who enable his mental disorder to satiate their own desires to hurt people. We are dealing with a large percentage of Americans who enjoy sadism at the expense of The Other, whoever that may be at any given time. We are a very sick country right now.