I used to think of Trump as a dangerous but recognizable demagogue. Now I see him as a genuine aberration in our history — and a unique threat to the nation.

A second Donald J. Trump presidency would almost certainly mark a return to an era of foreign policy decrees, untethered to any policy process, at a moment of maximum international peril.

A new memoir by the onetime national security adviser shows how the former president’s insecurities and weaknesses harmed U.S. foreign policy.