This dissertation offers a genealogy of political theory as a subfield of American political science. Over five chapters, it traces the subfield’s development from late nineteenth-century America until the 1970s and asks how leading practitioners responded to a series of political conjunctions. The first chapter asks how political theory emerged from the progressive movement and was characterized by a racist, “Teutonist” intellectual framework that lasted until the First World War. The war led to the demise of this initial framework, leaving political theory without an anchor. The second chapter asks how a leading political theorist, Charles Merriam, sought to resuscitate political theory by making it more “scientific,” focusing on analyzing political behavior. This chapter demonstrates how interaction with the city of Chicago forced Merriam’s thought into more egalitarian directions. The third chapter charts political theory in “the age of fear.” It shows how Merriam and his student Harold Lasswell sought to thicken liberalism and conceptualize its totalitarian alternatives. The fourth chapter asks how leading behavioralists—including Gabriel Almond, Robert Dahl, and David Truman, as well as Louis Hartz—deployed political theory to characterize, congratulate, and criticize the tenets of American liberalism in the context of the Cold War. In the project’s final chapter, I ask how political theory went its own way as a subfield. Amidst the tumult of the 1960s, its leading practitioners—including Sheldon Wolin and Leo Strauss—found themselves politically at odds with behavioralism. Their opposition to the practice of political science led them to associate humanism with radical political critique. By offering a history of political theory that puts behavioralism at its center, the dissertation unsettles conventional narratives within political science that characterize political theory as the other of “empirical social science.” Second, by highlighting a tradition of thought that married systematic empiricism and normative intent, the dissertation critically recaptures a realistic mode of political theorizing. Raymond Geuss has called for political theory to engage more with the facts of the political world. My dissertation offers a way forward. It reminds readers that empiricism can be a normative venture and highlights the close affinity between political science and theory. Many political scientists, I argue, were engaged in a project we can term “operational political theory.” They took theoretic concepts—such as democracy—and furnished them with empirical evidence. They asked how political theory worked in practice and then evaluated extant practices according to political theoretic norms.