Alliance Commitment in an Era of Partisan Polarization: A Survey Experiment of U.S. Voters

There is rising apprehension that U.S. partisan polarization is making it harder for the United States to keep its international commitments. This could have profound implications for one of the most critical elements of U.S. foreign policy: its commitment to its alliance partners. We explore this issue by analyzing to what extent partisanship can influence U.S. voter commitment to aid and defend allies. Using four survey experiments, the study analyzes the resilience of U.S. support for an ally, the Republic of Korea, across a range of scenarios. When presented with a neutral framing of South Korea without any overt partisan cues, voters support South Korea even at the risk of incurring military casualties or economic costs. Compared to Democrats, however, Republicans consistently express lower support for South Korea. These results suggest that there is a clear partisan divide when it comes to alliances. Furthermore, we find that stronger cues that target partisan group identities can trigger sizable effects on voter attitudes. Collectively, these results suggest that growing partisan polarization may increase uncertainty in U.S. voter commitment, a finding with important implications for the U.S.-South Korean alliance and alliance credibility more broadly.