It is often at moments of crisis that Americans get the clearest glimpses of a president’s character, and this week they had the chance to learn a good deal about the true Donald Trump after his abrupt decision to fire James Comey, the F.B.I. director.

Mr. Trump’s actions and the disclosures by those close to him revealed this president to be an insecure, fearful man who can’t eat or place a phone call without a backdrop of fawning aides. Rather than cultivate experienced, strong-minded advisers who might challenge his views, Mr. Trump prefers to govern by impulse and edict, demanding absurd pledges of “loyalty.”

Americans learned that Mr. Trump gave his bodyguard’s opinion on the Comey matter as much weight as any adviser’s, if not more. They saw that he was comfortable humiliating aides by flatly contradicting their accounts of his decision-making.

They saw, as many of them had no doubt suspected, that he has a limited understanding of, or respect for, the constitutional responsibilities of public officials. During a January dinner in the White House, in which Mr. Trump apparently tried and failed to extract a vow of loyalty from Mr. Comey, the president gave no sign of grasping the federal statute binding both men: “Public service is a public trust, requiring employees to place loyalty to the Constitution, the laws and ethical principles above private gain.” To Mr. Trump, “loyalty” meant abandoning an investigation into foreign interference in the last election.