This article first appeared at Just Security.
President-elect Donald Trump has promised to carry out the largest deportation operation in American history. While he has provided few specifics about how his administration would accomplish this, Trump has indicated that he will declare a national emergency and that he will invoke both the Insurrection Act and the Alien Enemies Act. A common theme in almost all of his statements is his intent to deploy the military.
The prospect of heavy military involvement in immigration enforcement has generated alarm in many quarters. But the authorities that Trump might summon—and the hurdles he might face in using them—are not widely understood. This article seeks to identify and elucidate them. Starting with the baseline constraint on military participation in law enforcement, the Posse Comitatus Act, the discussion below sets forth the relevant statutory authorities in escalating order of potency and identifies potential constraints on their use.
This article is intended as both a primer and a reference (i.e., readers can skip to the particular authorities about which they may have questions). The authorities covered may be summarized as follows:
- Chapter 15 of Title 10 of the U.S. Code has several provisions allowing federal armed forces (including active-duty forces and federalized National Guard forces) to assist with law enforcement, including through the provision of military facilities and equipment, without directly participating in core law enforcement activities.
- A declaration of national emergency under the National Emergencies Act could provide additional resources for military assistance to law enforcement but would not permit federal armed forces to participate in core law enforcement activities.
- 32 U.S.C. 502(f)(2)(A) allows the president to request (but not require) that governors deploy their states’ National Guard forces to perform certain federal missions, free from the constraints of the Posse Comitatus Act—i.e., Guard forces could participate in core law enforcement activities.
- The Insurrection Act, generally regarded as the primary statutory exception to the Posse Comitatus Act, allows the president to federalize National Guard forces and to deploy them and active-duty armed forces anywhere in the country.
- The Alien Enemies Act does not itself authorize military deployment, but when combined with the Insurrection Act or other authorities, it could permit the militarized deportation of immigrants lawfully in this country under specified conditions.
More on all of these authorities can be found on the Brennan Center’s “Domestic Deployment of the Military” and “Outdated and Dangerous” webpages.