I thought of the Comey book as well. A comment in an interview with Comey jumped out at me:
Leaders like President Bush and President Obama have, when they're making hard decisions, external reference points. They think about a religious tradition or philosophy or history of the law. My experience with Donald Trump is that the only reference point is internal: 'What will give me the affirmation I crave?' . . . That is disturbing in a leader.
Also, Timothy Snyder, in On Tyranny: "Don't obey in advance."