The H-Diplo/ISSF Policy Series asks, among other questions, what diplomatic history and international relations theory tell us about the future of the U.S. in the world. I attempt to answer from the historian’s side, by focusing on economic nationalism in the 1930s. The Smoot-Hawley Tariff of 1930 represents the most famous case of trade protectionism in American history, and President Franklin Roosevelt’s rejection of the World Economic Conference three years later added to the U.S. economic nationalist response to world affairs. Both issues inform us of the possible consequences of Donald Trump’s approach to the global economy. I think history offers some dismal lessons.