The literature on social policy expansion and retrenchment in Latin America is vast, but scholars differ in how they explain outcomes, arriving at different conclusions about the role of democracy, left parties, favorable economic conditions, and social movements. What can welfare state developments since the end of the commodity boom teach us about the theoretical power of these arguments? This paper engages this question, seeking to explain recent incidents of successful social policy reform in 10 presidential administrations in Argentina, Brazil, Chile, and Uruguay. Using a combination of crisp-set qualitative comparative analysis (csQCA) and case studies, we identify multiple paths toward successful social policy expansion and retrenchment. The QCA results highlight two key findings. First, social policy expansion was generally carried out by programmatic parties (often, though not always, from the left). Second, retrenchment is most likely when nonprogrammatic right parties face fiscal constraints. The case studies affirm these findings and show that differences in electoral competition, social movement pressure, and policy legacies shape the contexts in which expansion and retrenchment is feasible. The results provide new insight into social policy reform, underscoring the relevance of complex forms of causality.