Why is health reform so difficult to achieve in the US? When it does succeed, what factors contribute to its success? This paper extends a causal model presented last year to include political and other factors that help to answer these questions. The paper examines the experience of several states in the US as they have struggled with a key aspect of health reform, extending insurance coverage to children, families, and other groups that are uninsured. . It also draws from other models that have been applied to understanding political and social change. The causal analysis that is presented emphasizes the importance of making policy choices in shaping proposed reforms that fit within a “window of opportunity” presented by the state’s political and economic environment. The paper concludes by suggesting that expanding access must be viewed as an ongoing process in which early successes create opportunities to benefit additional people.