Challenging the Challengers? The Transformative Implications of the Bündnis Sahra Wagenknecht for German Party Competition

Abstract This article examines the transformative impact of a challenger’s entry into party competition, using a quasi-experimental design to provide an evidence-based evaluation of its effects on voter mobilization, competition with mainstream parties, and interactions with other challengers. Leveraging variation in the participation of the newly formed Sahra Wagenknecht Alliance ( Bündnis Sahra Wagenknecht [BSW]), we analyzed local elections in five German states. To account for strategic factors influencing BSW participation, we applied covariate balancing propensity scores to ensure comparability between treated and nontreated municipalities, enabling an unbiased estimation of the average treatment effect of BSW participation on changes in voter turnout and party vote shares. Except for the right-wing Alternative for Germany ( Alternative für Deutschland ) party, our findings reveal a significant reduction in vote shares for all parties, with no evidence of increased voter mobilization. These results have important implications for party competition dynamics and the functioning of representative democracy in the presence of multiple challengers.