I've bought several of the major Trump tell-all books, including FEAR, A HIGHER LOYALTY, FIRE AND FURY, EVERYTHING TRUMP TOUCHES DIES, and the audio-book version of THE MUELLER REPORT (even in audio, still a slog), but this is the one I would recommend most, if what you're looking for is a true-to-life glimpse inside the ongoing Trump trainwreck.
I believe the author is a Republican, and it's my experience that Republican authors who are critical of Trump can take you deeper into these people's minds