From the center to the fringes: A comparative test of attitudinal explanations for mainstream-to-challenger defection

The 2025 German Federal Election witnessed unprecedented levels of mainstream-to-challenger defection. Why did former mainstream supporters abandon the political center for the fringes? We contrast four theoretical explanations: general political frustration, positional representation, prioritization of issues “owned” by challengers, and differential performance evaluations. Moving beyond the conventional focus on effects, we assess the relative predictive reach of these explanations using Bayesian finite mixture models. Our analysis of the 2025 GLES Post-Election Cross-Section identifies the so far neglected importance of performance evaluations: beliefs that challengers are more capable political actors than their mainstream competitors consistently emerge as the strongest explanation of mainstream-to-challenger defection. This pattern even holds when accounting for the potential endogeneity of performance evaluations to the rival explanations. Our findings suggest that challengers, despite lacking executive experience, can mobilize support via subjective ascriptions of capability—challenging assumptions that mainstream parties’ accumulated reputational resources necessarily translate into electoral advantage.