Promoting the rule of the law is a national responsibility. The obligation to ensure legality and advance human rights rests on the national government. This article analyzes how federalism, a system of distributing power among subnational entities, can promote this national goal. The article explores how states in the United States have played an important role in encouraging the federal government to enforce the law and safeguard rights. By means of resistance, cooperation, and redundancy, states have moved the United States closer to rule-of-law ideals. The state action sometimes takes the form of litigation, with states bringing suit against the federal government. Such suits have particular significance in challenging illegal inaction by the national government, as when the federal government fails to enforce environmental laws. Litigation by states may overcome standing barriers that would limit such suits by private individuals. States may also engage in direct action by pursuing their own policies that promote the rule of law. In these areas, the states may oppose the federal government, cooperate with the federal government, or act in an independent, parallel manner. What unites all of these modes and instruments of state-federal interaction is that the goal of states is to influence national policy. The state action may begin within the boundaries of a particular state, but what motivates the state initiative is a vision applicable to the nation as a whole. The ultimate aim of state action is not local divergence, but national uniformity. Federalism serves not as a license for local deviation from national norms, but instead as a means for states to engage actively in creating policy at a national level. In this way, independent state activity can indeed promote the national obligation to promote the rule of law throughout the country.