In the aftermath of September 11th, policymakers, pundits, and international relations scholars alike all deemed nuclear terrorism a top security threat to the United States, with some even predicting that a nuclear terrorist attack was inevitable. In the two decades since the Twin Towers fell, however, the United States has not experienced such an attack. This generates an important question: Why did the United States misconstrue the threat of nuclear terrorism in the aftermath of 9/11 as greater than it has proven to be? This project proposes a three-fold theory to answer this question, arguing that decision makers exaggerated the threat on account of the shock of 9/11, a poor understanding of terrorists’ intentions and capabilities, and the existential nature of the threat. Ultimately, U.S. decision makers did not willfully manipulate or inflate the nuclear terrorist threat in the aftermath of September 11th, but rather, overestimated the threat for valid strategic reasons given the uncertainty of the international system.