In two fields of constitutional law, the Supreme Court has acknowledged that the federal government may possess preconstitutional power, or national authority derived not from the Constitution but from the very fact of sovereignty. This Article analyzes the two areas of law – the Foreign Affairs Power and the Indian Affairs Power – and assesses their viability in future cases. The case recognizing a preconstitutional Foreign Affairs Power resting with the Executive branch, United States v. Curtiss-Wright Export Corp., suffers from poor historical reasoning and has little precedential weight in modern foreign affairs cases, but has never been overruled. The Indian Affairs Power case, United States v. Lara, decided in 2004, included no historical reasoning and only offered the theory as dicta. However, the Court raised the theory, perhaps, as a means of placating the textualists on the Court who do not view the Indian Commerce Clause as a viable source of Congressional power in Indian Affairs. This Article offers a best defense for the proposition that Congressional plenary power in Indian Affairs might derive from a preconstitutional source, a defense that includes the original understanding of the Indian Affairs Power and that, unlike the Foreign Affairs Power, did survive the ratification of the Constitution.