Mexico and the United States exercise sovereignty that is increasingly transnational and less absolute with respect to migration. This is evident in changes to Mexico’s norm of non-intervention and the United States’ plenary power doctrine, two doctrines rooted in international sovereignty. Both have historically defined sovereign authority in absolute terms, avoiding any foreign influence or domestic limitation. The non-intervention norm prohibits Mexican foreign relations from interfering in another state’s domestic affairs. Traditionally, it barred a foreign policy on migrants in the United States, which led to Mexico’s “no policy” on migrants. The U.S. plenary power doctrine labels immigration law as immune from judicial review because the political branches have complete, “plenary” authority over it. Traditionally, the plenary power doctrine barred constitutional limitations to this migration authority.
Since 2001, two events have occurred that indicate a slight migration from the plenary power doctrine and non-intervention norm’s traditional conceptions of sovereignty. First, in Zadvydas v. Davis, the U.S. Supreme Court explicitly stated that the plenary power doctrine is “subject to important constitutional limitations.” Second, Mexico has actively lobbied U.S. lawmakers for reforms to U.S. immigration laws, an effort sometimes called the “whole enchilada.” These developments lead to the opposite conclusions espoused by each doctrine: that there are constitutional limits to the plenary power doctrine and that foreign relations may influence another state’s lawmaking.