A common explanation for the increasing polarization in contemporary American foreign policy is the absence of external threat. I identify two mechanisms through which threats could reduce polarization: by revealing information about an adversary that elicits a bipartisan response from policymakers (information mechanism) and by heightening the salience of national relative to partisan identity (identity mechanism). To evaluate the information mechanism, study 1 uses computational text analysis of congressional speeches to explore whether security threats reduce partisanship in attitudes toward foreign adversaries. To evaluate the identity mechanism, study 2 uses public opinion polls to assess whether threats reduce affective polarization among the public. Study 3 tests both mechanisms in a survey experiment that heightens a security threat from China. I find that the external threat hypothesis has limited ability to explain either polarization in US foreign policy or affective polarization among the American public. Instead, responses to external threats reflect the domestic political environment in which they are introduced. The findings cast doubt on predictions that new foreign threats will inherently create partisan unity.

The literature on immigration is divided between theories that highlight the importance of prejudice and theories that emphasize realistic threat as the primary driver of anti-immigration attitudes. This study examines how prejudice and realistic threat impact White Americans’ attitudes toward accepting refugees and immigrants in general. Using data from the 2016 American National Election Study and the 2016 Chicago Council Survey, I show that even though refugees differ from other immigrants in terms of their legal status and the rhetoric pertaining to them, attitudes toward immigration policies relating to both refugees and immigrants in general are primarily driven by prejudice.