After a week during which 13 packages containing explosive devices were intercepted on their way to prominent figures associated with the Democratic Party, authorities arrested suspect Cesar Sayoc on Friday. Although the apprehension may lead to some answers, authorities have warned that more mail bombs could still be working their way through the postal system, and the questions and anxiety that filled many Americans’ minds this week are unlikely to have abated. For Beverly Gage, a professor of history at Yale and the author of The Day Wall Street Exploded: A Story of America in Its First Age of Terror, which examines an anarchist bombing that took place in 1920, the week’s news has also brought something else to mind: a spate of package bombs that frightened the nation almost exactly a century ago, around May Day of 1919. Targets included John D.