1) We’ve just gotten lucky. That’s the case Will Saletan made for Slate yesterday, after running through the F.B.I.’s list of cases involving explosives going back to the beginning of 2012. He found plenty of intercepted plots against soft targets (malls, synagogues, restaurants, etc.), several cases where only a last-minute break prevented the plot from going forward, and plenty of plotters canny enough to cobble together their devices out of ordinary household materials. ”When you look at the 20 cases,” Saletan writes, “you realize that Boston is just the tip of the iceberg. What’s surprising isn’t that the marathon bombing succeeded, but that so many other plots failed.” And given the combination of an expanded target list and the ongoing innovations of bombmakers, he suggests, we should expect more of them to succeed in the future. …

3) It’s the End of History. This is an argument I’ve made myself: Namely, that with the collapse of grand ideological alternatives to liberal democracy one would expect terrorism to become mostly the province of madmen and nihilists and eccentric loners, rather than more purposeful movements and organizations. Call it the Christopher Nolan thesis, if you don’t care for Francis Fukuyama: In a world where the major ideological debates have either been resolved or set aside, terrorism becomes the province of people who, Joker-style, “just want to watch the world burn,” which means that we have lots of one-off horrors and senseless-seeming massacres but fewer agenda-driven terror campaigns.