Should mainstream parties systematically rule out coalitions with radical right-wing parties to avoid legitimizing their rhetoric, or do such exclusionary strategies inadvertently increase support for the radical right by fueling voter resentment? Addressing this question empirically is challenging because mainstream parties’ strategies are often endogenous to the electoral success of radical right parties, rather than an independent cause. This article tackles this empirical challenge by leveraging changes in the way Austrian Länder executives are elected, with five of the nine states transitioning from Proporz—a system guaranteeing all represented parties above a certain threshold a share of executive power—to a more conventional majority system, which allowed for the exclusion of the radical right FPÖ. Using a staggered Difference-in-Differences framework and accounting for heterogeneous treatment effects, we analyze elections in Austria’s nine Länder from 1980 to 2021. We find that the change to majority rule was associated with increased electoral support for the FPÖ in excluded regions. Our findings contribute to the broader debate on whether exclusion or engagement with the populist radical right is the more effective strategy to limit their electoral appeal.