The conventional account of American diplomacy in the modern era is marked by a cultural tension between realist and idealist themes symbolized by the statecraft of Theodore Roosevelt and Woodrow Wilson. However, a revisionist account has emerged to challenge and even reverse the conventional account of Roosevelt and Wilson. This poses an intriguing empirical puzzle that is essentially psychological, as it pertains to the belief systems of these two presidents. In order to investigate this puzzle and its implications for U.S. strategic culture, we employ an automated content analysis of the public statements by the two leaders regarding their operational code beliefs about the nature of the political universe and the best approach to effective political action. The results reveal similarities and differences in their belief systems and illustrate how psychological models can provide insights into the psychocultural origins of U.S. diplomacy that remain relevant to the present day.