Donald Trump is committed to being a victim. He is always being misunderstood and subject to unfair treatment by the Democrats, media, and “deep state.” The psychological function of holding oneself out as a martyr is to reassure oneself and the world that one is not guilty or ashamed, that one is innocent. Secondarily, however, victimhood enables one to continue to do hurtful and bad things. It’s like a “get out of jail free card.” Since one is being victimized, anything goes; any hostile or aggressive action is justified. Given that Trump feels he’s always getting a raw deal from everyone, he’s entitled to retaliate, meaning he’s entitled to do bad and harmful things (which he does). Impeachment is especially provocative for him since it’s a public accusation that he’s done bad things. As a result, he feels sadistic rage which then makes him have to present himself as even more of a victim.