Three times in this century the US public has panicked with fear because of exaggerations of external threats to the nation. These panics peaked in 1950,1960, and 1980. Why did the U.S. markedly exaggerate the Soviet threat at these times? These periods of widespread public fear were "defining moments" when the US created confrontational and militarized containment policies. These panics ratcheted up the arms race tremendously between the US and the Soviet Union, and arguably these panics led to unnecessary confrontations and crises. In this study I test leading explanations of these cases--eight hypotheses drawn from three different perspectives. The Rational Perspective argues insufficient information and uncertainty about present and future capabilities and intentions causes overestimations. The Psychological Perspective argues cognitive errors could cause these overestimations (attribution theory and schema theory/analogical reasoning, tested here). The Domestic Politics Perspective argues oversell, logrolling, electoral politics and/or militarism causes public overestimations. Domestic Politics best explains the national misperceptions examined. In each case, the sources of the specific misperceptions examined were clearly rooted in domestic politics (1950: oversell and militarism; 1960 and 1980: electoral politics and militarism.) Uncertainty about the threat was found to be a significant contributing factor in 1950 (but not the source/elites did not unintentionally overestimate when the misperceptions first formed).