Postindustrialization and occupational change considerably complicate partisan politics of the welfare state. This article asks about the determinants of contemporary social democratic labor market policy. We argue that the composition of their support base is a critical constraint and empirically demonstrate that the actual electoral clout of different voter segments decisively affects policy outcomes under left government. We calculate the electoral relevance of two crucial subgroups of the social democratic coalition, labor market insiders and outsiders, in 19 European democracies and combine these indicators with original data capturing the specific content of labor market reforms. The analysis reveals considerable levels of responsiveness and demonstrates that relative electoral relevance is consistently related to policy outcomes. Social democratic governments with a stronger support base among the atypically employed push labor market reforms on their behalf—and vice versa. Our findings have important implications for our understanding of policy-making in postindustrial societies.