I’ve kept a copy of Timothy Snyder’s book "On Tyranny" on my desk since it was published, in 2017. It’s a small volume-the cover is about the size of an index card. Most of the time, it’s buried under stacks of paper from stories I’ve been working on. Snyder is a historian of the Holocaust and of fascism, at Yale, and this book, subtitled "Twenty Lessons from the Twentieth Century," is a claxon rung to get our attention. "Listen up," Snyder seems to be saying to Americans. "Tyranny, fascism, authoritarianism could happen here, too."