It has always been true that foreign policy debates tend to proceed on a weak evidentiary base, with clever quips or stirring oratory regularly trumping sound analysis. According to Thucydides, for example, the Athenian assembly that endorsed the Sicilian expedition during the second Peloponnesian War had only the haziest conception of the adversaries' capabilities. Contemporary politics is distinctive not in the sloganeering quality of political discourse, but in the divergence between the quality of information available to society as a whole and the quality of information used in making decisions. For example, it was clear to any open-minded observer by the time of the Congressional vote in 2002 that implications of collaboration between Saddam Hussein and al-Qaeda lacked any basis in reliable evidence. By the time the Bush Administration initiated war in 2003, claims about Iraq's nuclear, chemical, and biological weapons capabilities were also partially debunked and increasingly dubious. Still, the war went forward, and many Americans continued to believe the Bush Administration's false claims even after the Administration itself had abandoned them.Patrick Thaddeus Jackson is Associate Professor of International Relations in the School of International Service at the American University in Washington, DC (ptjack@ american.edu). Stuart J. Kaufman is Professor of Political Science and International Relations at the University of Delaware (skaufman@udel.edu). For helpful comments and feedback on this article, we would like to thank Monica Duffy Toft, Neta Crawford, Daniel Nexon, and three anonymous reviewers.