In both Hamdan v. Rumsfeld and Sanchez-Llamas v. Oregon, government briefs asserted that there is a “long-established presumption” that treaties do not create judicially-enforceable individual rights. In his dissent in Sanchez-Llamas, Justice Breyer challenged this claim. The debate about whether the Supreme Court should adopt such a presumption is part of a broader conflict between the “nationalist” and “transnationalist” models of treaty enforcement. The transnationalist model applies a presumption in favor of domestic judicial remedies for violations of treaty-based individual rights. In contrast, the nationalist model applies a presumption against individual remedies for treaty violations. This article analyzes the historical foundations of both models. It demonstrates that doctrines involving the domestic judicial enforcement of treaties have changed dramatically in the past thirty years. Between 1789 and 1975, there was not a single judicial decision endorsing the nationalist presumption against private enforcement of treaty rights. In contrast, there were dozens of Supreme Court decisions that applied the transnationalist presumption in favor of domestic judicial remedies. Although the nationalist presumption against individual enforcement of treaties has gained widespread acceptance in the lower courts in the past thirty years, the Supreme Court has never endorsed that presumption. The Court’s decisions in Hamdan and Sanchez-Llamas declined to endorse either the nationalist or transnationalist presumption, but the Court’s ultimate resolution of the conflict between the nationalist and transnationalist models will have significant implications for U.S. foreign relations, separation of powers, and the rule of law.