Previous research on the role of ethnic minority interest groups in US foreign policy has resulted in the development of an extensive list of criteria thought to condition ethnic minority influence. Existing case studies, in spite of their significant contribution, leave open the question of which factors, if any, actually drive influence. The result is a foreign policy decision-making puzzle. We know that ethnic minority groups attempt to influence foreign policy. We also know that foreign policy decision makers sometimes choose the option favored by certain ethnic minority groups. What practitioners and scholars alike do not know is whether decision makers make choices because of the efforts of ethnic minority groups. The experimental designs presented in this study offer the opportunity to solve the puzzle by isolating the impact of diasporic interests on foreign policy decision making at the congressional level. Using a hypothetical foreign policy scenario, the study examines the independent and interactive effects of diasporic numerical significance, diasporic mobilization, and cultural similarity on foreign policy decision making. Results indicate that decision makers are highly responsive to diasporic mobilization, but were unresponsive to diasporic numerical significance and cultural similarity. The overall implication is that small, but highly mobilized, ethnic minority interest groups may be able to significantly influence the development of US foreign policy at the congressional level.