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Walking the Line: The Use of Military Personnel to Secure the U.S.-Mexico Border

By: Daniel de Zayas

As 2018 marches to a close, a migrant caravan marches closer to the U.S.-Mexico border, seeking asylum for approximately 5,000 Central Americans. President Trump has condemned the caravan, even referring to it as an “invasion,” and has deployed approximately 6,000 military troops and 2,000 National Guard soldiers to help the U.S. Border Patrol Service secure the border. Preparing for the caravan’s arrival, troops have installed barriers and barbed wire, conducted aerial reconnaissance and transport, and erected command and logistics facilities. Moreover, the Trump administration recently authorized the troops to engage in “protective activities that the Secretary of Defense determines are reasonably necessary to ensure the protection of federal personnel, including a show or use of force (including lethal force, where necessary), crowd control, temporary detention, and cursory search.” These developments raise concerns whether the military’s deployment to the border contravenes the Posse Comitatus Act (PCA), which precludes the willful use of military personnel for domestic law enforcement unless expressly authorized by Congress or the Constitution.

The PCA specifically delineates the following prohibition:

Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army or the Air Force as a posse comitatus or otherwise to execute the laws shall be fined under this title or imprisoned not more than two years, or both.

Although the PCA appears relatively clear on its face, its scope has been carefully interpreted and refined throughout history. Originally passed in 1878 as a bitter rebuke to the deployment of the army to supervise southern state elections, the PCA initially only barred the use of the Army for domestic law enforcement. Subsequent amendments and regulations have extended the PCA to bar the use of the Air Force, Navy, and Marines for domestic law enforcement. However, both the Coast Guard and the National Guard are generally exempt from the PCA.

Further defining the PCA’s scope, federal district courts have identified three forms of military involvement that violate the PCA. First, in United States v. Jaramillo, the U.S. District Court for the District of Nebraska held that military involvement that “pervade[s] the activities” of civil law enforcement violates the PCA. Second, in United States v. Red Feather, the U.S. District Court for the District of South Dakota held that the Act proscribes active, direct military involvement, such as interviewing witnesses, searching persons, seizing evidence, and making arrests. Conversely, the court found that the Act permits passive, indirect involvement, such as advising civilian law enforcement, delivering and maintaining equipment, and conducting aerial reconnaissance. Third, the U.S. District Court for the District of North Dakota in United States v. McArthur held that military involvement that subjects citizens to “regulatory, proscriptive, or compulsory” power violates the PCA. These decisions indicate that the use of military personnel to support civil law enforcement does not violate the PCA.

The PCA recognizes several exceptions, statutory and constitutional, that permit the use of military personnel for domestic law enforcement. For example, the Insurrection Act of 1807 authorizes the president to deploy troops to “any insurrection, domestic violence, unlawful combination, or conspiracy” that opposes or obstructs civil law enforcement or impedes justice. Similarly, Congress codified several “passive, indirect” support activities identified in Red Feather as statutory exceptions. Alternatively, the president may invoke a constitutional exception—the inherent powers doctrine—to defend national security. However, there is an ongoing debate about whether the inherent powers doctrine, only implicit in the Constitution, satisfies the PCA’s “expressly authorized” condition.

Applying the PCA framework, the deployment of U.S. troops to the border to conduct support activities does not violate the Act. Installing barriers and building facilities likely constitute passive, indirect military involvement permissible pursuant to both Red Feather and statutory exception. Similarly, aerial reconnaissance conducted by U.S. troops is expressly permissible under both Red Feather and statutory exception.

However, U.S. troops at the border may violate the PCA if they engage in the “protective activities” authorized by the Trump administration. Temporarily detaining migrants and conducting cursory searches likely constitute active, direct military involvement proscribed by Red Feather or, alternatively, an exercise of “regulatory, proscriptive, or compulsory” military power proscribed by McArthur. Similarly, pursuant to Jaramillo, crowd control may unlawfully “pervade[] the activities” of civil law enforcement. Moreover, the U.S. troops may only use lethal force in self-defense, which requires a “reasonable belief that the subject of such force poses an imminent threat of death or serious bodily harm” and prohibits the use of excessive force under the totality of the circumstances.

Conflicting reports from the Trump administration leave uncertain whether the military presence is justified by its supportive nature, or whether it is postured upon statutory or constitutional exception. The Trump administration seems to be framing the caravan to implicate the Insurrection Act of 1807, emphasizing that the caravan’s size and alleged presence of 500 migrants with criminal records increases the likelihood of violence and disorder. If, however, President Trump invokes his inherent powers, the world must carefully monitor the legality of the military activities as both the caravan and executive power reach their respective borders.


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