The main theories explaining electoral backlash against immigration focus on citizens’ cultural, economic, and security concerns. We test these predictions in Switzerland, which opened its labor market to neighboring countries in the 2000s. Employing a difference-in-differences design, we document a substantial rise in immigrant workers in Swiss border municipalities after the border opened. This was accompanied by a 6-percentage-point (95% confidence interval 2–10) increase in support for anti-immigrant parties, equivalent to a 32% rise at the mean. However, we find no adverse effects on citizens’ employment, wages, or subjective perceptions of economic, cultural, or security threats. Instead, we describe how far-right parties introduced novel narratives related to overcrowding to advance hostility toward immigrants. We provide evidence that this rhetoric targeted border municipalities, where it had the greatest impact on voters susceptible to political persuasion. Together, these findings suggest that elites can play a role in driving anti-immigrant votes.