Research on social movements has illuminated when and how they influence policy formulation, but less is known about what shapes the durability of those policies once adopted. Why do some victories endure while others erode? Drawing on the process-tracing of seventeen movements around mining conflicts in Ecuador and Peru during the 2000s commodity boom, we argue that post-adoption politics are critical. Policy durability requires movements to sustain pressure both from civil society and the state. Beyond sustained mobilization power, durable full gains hinge on two strategic objectives: leveraging a decision point in regulatory agencies and securing a favorable ruling from a higher-level authority such as the presidency or high courts. Movements achieving only the former attain temporary partial gains; lacking both leads to defeat.