It’s part of a broader trend in the capital’s recent history that gets a lot less attention: A new, and dizzying, sense of vulnerability in a city that used to think history only happened to other people. For years, a lot of people in professional Washington may have worked on issues involving danger or violence or trauma around the country and the world. But for the most part, those things were taking place elsewhere. Domestic rivals and geopolitical enemies were not going to menace them on their commute home. Sure, the region suffered the same pathologies as the rest of...