How does ballot structure affect party choice? We argue that open lists undermine the electoral support of cohesive parties, to the benefit of internally divided parties. We conduct a survey-embedded experiment in the aftermath of the European migrant crisis, presenting German voters with real parties but fictitious politicians. A crossover design varies ballot type and exposure to candidate positions on immigration. We find that the internally divided Christian Democrats gain votes at the expense of the cohesive Alternative for Germany when open lists are used and candidate positions are known. For individuals who are equally attracted to both parties, switching is most likely if their immigration preferences lie near the midpoint between the two parties. Overall, our analysis establishes conditions under which ballot structure can affect the electoral performance of parties in general, and that of the populist right in particular.
