Red Lines That Bind: International Law and Domestic Political Audiences in U.S. Counterproliferation Policy

When, for whom, and why does the international lawfulness of military force affect the credibility of coercive threats? The credibility of coercion largely hinges on the domestic political costs that leaders incur for making, backing down from, or acting upon foreign threats (domestic audience costs). Doctrinal legal research investigates the international lawfulness of the threat and use of force, while an extensive body of international security literature examines domestic audience costs through vignette survey experiments. However, no studies have directly evaluated the effects of international law on domestic audience costs.

In my thesis, I present a representative sample of the U.S. public with a vignette survey on a hypothetical foreign policy crisis: Iran is on the brink of developing nuclear weapons, and the U.S. President issues a deterrent threat against an Iranian nuclear weapons test. The various treatment scenarios presented in the survey vary by three factors: the stated international lawfulness of the U.S. President’s threat, the President’s subsequent decision to either follow through or back down after Iran conducts a nuclear weapon test, and—when the President follows through—the success or failure of the ensuing military engagement. My data demonstrate that the stated international legality of the counterproliferation threat and whether the President followed through on the threat affects respondents’ political support for the President and perceived levels of reputational damage. There are no observable domestic audience costs for an internationally lawful counterproliferation threat, with backing down from an internationally unlawful threat resulting in more political support from respondents compared to staying out (domestic audience benefit). Moreover, varying the international lawfulness of threats resulted in notable divergence in the effects of inconsistency and belligerence, with the U.S. public’s preferences for counterproliferation offsetting perceived reputational damage for making such threats. Depending on the treatment, respondents’ individual-level characteristics and assumptions help explain their political support for the President. My findings provide valuable insights for policymakers considering the effects of international law on domestic political support for coercive threats.