This article examines the evolution of humanitarian interventions in the 1990s and examines whether or not R2P can be a catalyst for shifting the norm of humanitarian intervention from a permissive condition – whereby it is generally considered allowable in the international system – to an obligation on states to protect against mass violence against civilians. I conclude that shifting to a norm of obligation is likely to be a tough sell in the United States. While Americans express general support for responding to genocide, there are strong indications that both the public and elites are not likely to endorse a new norm that obligates the deployment of American troops into regional and civil conflicts around the globe. This article examines the prospects of American support for this pillar of R2P. It begins with an examination of the literature on how norms are created and then provides an overview of the process by which the norm of humanitarian intervention emerged in the 1990s and the degree to which it is embedded in American public opinion and decision-making circles. It then examines the challenges of gaining American public and political support for transforming the permissive norm of humanitarian intervention into a more formal obligation under R2P.