Timothy Snyder's On Tyranny is a timely how-to guide for Westerners who fear the rise of totalitarianism. The first half of the book catalogs the early-warning signs that Snyder, a Yale historian, has spent decades studying. "Do not obey in advance." "Beware the one-party state." The second takes direct aim at Donald Trump, whom Snyder sees as the heir to the twisted Nazi logic of the 1930s. "The danger we now face is of a passage [towards] a confused and cynical sort of fascist oligarchy." Trump has not yet burned down the Reichstag, and tyranny is hardly the exclusive preserve of the right. But, like Hannah Arendt before him, Snyder is connecting all of the right dots.