"America First" brings both political weakness and moral hazard. The last episode was about America's new weakness in the world. This one is about how "America First" leads Americans to turn against one another.

Timothy Snyder is a historian at Yale University, specializing in eastern Europe, totalitarianism, and the Holocaust. His books have received widespread acclaim. His most recent book, "On Tyranny: Twenty Lessons from the Twentieth Century," explores the everyday ways a citizen can resist the authoritarianism of today. He is also the author of "Black Earth: The Holocaust as History and Warning" and, forthcoming in April, "The Road to Unfreedom: Russia, Europe, America."

Follow on Twitter: @TimothyDSnyder