Constitutional Limits on States’ Power over Foreign Affairs

"The Constitution gives the federal government the primary power to manage the United States’ foreign relations. Article I, Section 10 prohibits states from engaging in a set of activities that implicate international affairs, while the Supremacy Clause, Foreign Commerce Clause, and other constitutional provisions place key elements of this power with the federal government. Interpreting these provisions, the Supreme Court has described the United States’ foreign affairs power not only as superior to the states but residing exclusively in the national government. With respect to foreign relations, the Supreme Court said that “state lines disappear” and the “purpose of the State ... does not exist.”

Despite this sweeping language, states and other subnational entities (e.g., cities and counties) play a more prominent role in international relations than may be generally recognized. States have offices overseas and send trade and diplomatic delegations to foreign countries. They have imposed economicsanctions for human rights abuses and military aggression—most recently on Russia for invading Ukraine. States regularly enter into written pacts with foreign governments on issues ranging from trade to the environment to tourism.  Some of these international pacts address potentially sensitive subjects, such as border security with Mexico and technology transfers with the People’s Republic of China (PRC). A recent rise in pacts with PRC-based bodies led U.S. intelligence officials to warn state and local governments about PRC efforts to exploit its relationships with subnational governments to promote its geopolitical interests in the United States.

The Supreme Court has held that the Constitution constrains states’ ability to act on the global stage, but much of the state-driven international activity is not publicized or presented to Congress. Because Congress may have an interest in optimizing and overseeing states’ actions in this area, this Sidebar discusses constitutional limits on states’ role in international affairs and potential avenues for congressional involvement..."
States and Foreign Affairs