No matter what issue we think matters in the preservation of basic American interests, from Syria to Mexico, climate matters intensely. To deny climate change is not only to practice the politics of the big lie, it is to doom the country to irrelevance, impotence, and tremendous suffering. This will be the real test for our new secretary of state: will he continue to be a lobbyist for the energy industry, or will he serve the country?

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, "The Road to Unfreedom: Russia, Europe, America," tells the whole Russia story, from beginning to end, in a way that makes sense and reveals the big picture. He is also the author of "On Tyranny: Twenty Lessons from the Twentieth Century," which explores the everyday ways a citizen can resist the authoritarianism of today. His other works include "Black Earth: The Holocaust as History and Warning" and "Bloodlands: Europe Between Hitler and Stalin."

Follow on Twitter: @TimothyDSnyder

The Mueller investigation is not a contest of men but of principles. It is a contest between two ways of seeing the world, the outcome of which will very possibly determine whether or not the notion of an American republic makes any sense. This lecture is not about the details of the investigation, but about its wider sense and meaning for the future of the country.

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, "The Road to Unfreedom: Russia, Europe, America," tells the whole Russia story, from beginning to end, in a way that makes sense and reveals the big picture. He is also the author of "On Tyranny: Twenty Lessons from the Twentieth Century," which explores the everyday ways a citizen can resist the authoritarianism of today. His other works include "Black Earth: The Holocaust as History and Warning" and "Bloodlands: Europe Between Hitler and Stalin."

Follow on Twitter: @TimothyDSnyder