Foundation for Defense of Democracies (FDD) is an American think tank that has the most important role in shaping US republicans’ foreign policy. The current study focuses on the role of FDD in shaping US foreign policy against Iran. This study follows a descriptive-analytic method to content-analyze FDD’s the published reports on Iran. The present study also adopts a statistical approach to calculate the weight and share of Iran related reports that are published at this think tank. The results indicate that FDD’s policy against Iran, including the eight categories of Iran Global Threat Network, Iran Human Rights, Iran in Latin America, Iran Missiles, Iran Nuclear, Iran Politics and Economics, Iran Sanctions and Iran-backed Terrorism, considerably influenced Trump administration’s decision to withdraw the 2015 Joint Comprehensive Plan of Action (JCPOA). Finally, the application of game theory and FDD's strategy analysis shows that this think tank's desired strategy against Iran is to trigger the snapback mechanism and withdraw from the Joint Comprehensive Plan of Action (JCPOA), but the option that results in an equilibrium state between the US and Iran's relations is conducting negotiations and turning back to the JCPOA.