OLC’s Dangerous, and Wrong, Opinion About the Posse Comitatus Act

On Aug. 14, the Department of Justice Office of Legal Counsel (OLC) released an opinion concluding that military personnel can arrest individuals who unlawfully enter a national defense area (NDA) after they have left the NDA. Although the opinion stipulates that military personnel would operate “in the immediate vicinity of the NDA,” the opinion’s logic has dangerous ramifications. Its analysis of the Posse Comitatus Act (PCA) is also wrong.

Background

Since the beginning of the second Trump administration, the Defense Department has created six NDAs across the southern border. An NDA is composed of land turned over to the Defense Department that is then incorporated into existing military installations near the southern border. Since April 2025, the military has arrested hundreds of individuals within these NDAs for criminal trespass, thereby quite literally militarizing large sections of the southern border.

The Posse Comitatus Act (PCA), enacted in 1878, criminalizes using any part of the active-duty military “as a posse comitatus or other to execute the laws” unless “expressly authorized” by statute or the Constitution. As the OLC recognized in an opinion issued during the first Trump administration, courts have developed three tests implementing this prohibition. Traditionally, OLC has applied all three of these tests to assess whether a given activity violates the act. In one, the U.S. Court of Appeals for the Eighth Circuit held that the PCA prohibits activity that “actually regulates, forbids, or compels some conduct.” In another, courts concluded that the PCA prohibits “the direct active participation of federal military troops in law enforcement activities.” And in the last, most expansive, approach, courts inquired into whether the military activity “pervades the activities of civilian officials.”

In a sign of things to come, the OLC cites none of these cases in its present analysis. Neither does reference, at all, to OLC’s long-standing practice of applying all three tests to proposed military activity. And it does not cite, again unlike in the first Trump administration, Laird v. Tatum, the most recent Supreme Court case to consider the PCA in significant detail. Instead, if relies on a 1978 memo that predates much of this case law to stand for the proposition that the PCA only “precludes ‘military personnel [from] applying force to the civilian community in the normal course of civil government’ and prevents ‘actual or threatened coercion by persons subject to military discipline on behalf of civil law enforcement officers.’” This, of course, creates the illusion that the relevant legal standard is far less onerous than it actually is.

The OLC’s Opinion

The OLC’s Aug. 14 opinion relies on both a statutory exception to the PCA and a long-standing implied exception—the military purpose doctrine.

Statutory Exception

The OLC argues that 10 U.S.C. § 2672 is a statutory basis for the military to conduct off-base arrests. To reach this conclusion, it engages in confounding statutory interpretation that abandons traditional approaches to implementing the PCA.

Section 2672 requires that the secretary of defense “protect the buildings, grounds, and property that are under the jurisdiction, custody, or control of the Department of Defense and the persons on that property.” To carry out this duty, the statute authorizes the defense secretary to “designate military or civilian personnel of the Department of Defense as officers and agents.” These personnel are, in turn, authorized to “enforce Federal laws and regulations for the protection of persons and property,” carry weapons, make arrests (within certain limits), serve warrants and subpoenas, and conduct investigations. Before executing these tasks, the secretary must make a number of findings about the necessity of using departmental personnel for these purposes.

Importantly, the statute distinguishes how the secretary may use civilian and military Defense Department personnel. Only with respect to civilian personnel does the statute authorize the secretary to specify which, if any, of the authorized functions are “to be exercised outside the property” of the Defense Department. In a section labeled “Authority Outside Federal Property,” the statute provides that the secretary may “enter into agreements with Federal agencies and with State, Indian tribal, and local government to obtain authority for civilian officers and agents ... to enforce Federal laws and State, Indian tribal, and local laws” (emphasis added). And the statute requires that the secretary “consult with ... local law enforcement agencies” before “authorizing civilian officers and agents” to exercise off-base law enforcement jurisdiction (emphasis added).

This text does not, however, provide independent authority for the military to conduct off-base activity. The OLC seems to implicitly recognize this fact by changing the goalposts later in the opinion. Instead of seeking what the statute authorizes military personnel to do, it investigates whether the statute prohibits the military from performing off-base duty. OLC argues, for example, that the above sections regarding civilian off-base duty should “not [be] read ... as prohibiting all off-base protective activities by military officers who are fulfilling on-base assignments.” And it relies on the statute’s savings clause to argue that the statute does not, in the statute’s words, “restrict any other authority of the Secretary of Defense or the Secretary of a military department.”

Neither of these arguments, however, reveals anything about what the statute authorizes. A statutory exception to the PCA must be “express[].” As the OLC in the first Trump administration recognized, “for a statute to authorize a military activity expressly ... it must be clear that Congress has approved that activity without regard” to the PCA’s restrictions. Section 2672 expressly authorizes the military to perform specified law enforcement activities to protect Defense Department property. But in every instance where these activities are conducted off-base, the statute only references civilian Defense Department personnel. In light of the statute’s savings clause, this doesn’t suggest the statute prohibits military personnel from performing otherwise authorized off-base activities. But it cannot be read as a “clear” authorization for military personnel to perform these activities off-base without regard to the PCA.

In this way, § 2672 is similar to a statute authorizing Defense Department assistance to Customs and Border Protection (Section 1059 of the National Defense Authorization Act for Fiscal Year 2016), which the first Trump administration’s OLC found likewise did not constitute an express PCA exception. Congress knew how to authorize the secretary to protect Defense Department property from locations outside that property. It authorized the secretary to enter into agreements with other federal, state, and local law enforcement agencies to do so. And it clearly authorized the department’s civilian personnel to do so. But the statute says nothing about military personnel performing these same duties outside of military installations. Being silent, it cannot at the same time “clearly” authorize off-base activity.

Military Purpose Doctrine

The OLC’s analysis with respect to the military purpose doctrine is also incorrect. Defense Department regulations assert that “[a]ctions taken for the primary purpose of furthering a DoD or foreign affairs function of the United States” are not subject to the PCA’s restrictions. Importantly, the same policy provides that “[t]his does not include actions taken for the primary purpose of aiding civilian law enforcement officials or otherwise serving as a subterfuge to avoid the restrictions” of the PCA. As used here, OLC’s opinion does both.

As I have observed elsewhere, the modern construction of this implied exception to the PCA is of relatively recent vintage. The earliest such articulation of which I am aware dates to a 1977 Justice Department memorandum. Elements of the doctrine, however, are quite old. As OLC correctly notes, for example, since the early 19th century the executive branch has asserted a base commander’s authority to arrest and detain individuals while on military installations who disrupt the good order and discipline of that base. And courts have recognized this on-base authority in multiple cases.

Courts have not, however, recognized a similar exception for military personnel conducting off-base law enforcement activity with respect solely to civilians. The OLC cites three cases to support its position: United States v. Chon, United States v. Hitchcock, and Applewhite v. United States Air Force. Each varies from the current Defense Department proposal in material respects.

In United States v. Chon, the U.S. Court of Appeals for the Ninth Circuit found that agents of the Naval Criminal Investigative Service (NCIS), did not violate the PCA in their investigation of the on-base theft of Defense Department property in part because it had a military purpose. The complained-of activity, however, was an NCIS investigation conducted in conjunction with non-Defense Department civilian law enforcement agencies (primarily, the FBI). And, though the court found that it did not matter for the purposes of Chon, unlike the military personnel at issue now, NCIS is a civilian, not a military, law enforcement agency.

In United States v. Hitchcock, the Ninth Circuit again referenced the military purpose doctrine. There, the Army Criminal Investigation Division assisted with the investigation of a U.S. Marine on drug charges. This investigation led to the Marine identifying Hitchcock, a civilian, as the drug supplier. Importantly, Hitchcock was then investigated and arrested by the Drug Enforcement Administration. The court’s determination that the Army did not violate the PCA hinged on the fact that the Uniform Code of Military Justice (UCMJ) prohibits military personnel from possessing or distributing drugs. Hitchcock’s investigation was incidental to this statutorily authorized military investigation and conducted primarily by a coordinate civilian law enforcement agency.

The same was true in Applewhite v. United States Air Force. There, the Air Force Office of Special Investigations (OSI) conducted a counterdrug sting operation targeted at enlisted military personnel while at an off-base apartment. During one such sting, against Airman Applewhite, OSI officers conducted a pat-down search of his civilian wife, who was also present. She was found to have drugs and brought back to the base for further search and questioning. When the local police declined to participate in the investigation, OSI officers released Applewhite’s wife and no charges were brought against her. Here, again unlike in the NDA context, the investigation and subsequent sting were authorized by statute (that is, by provisions of the UCMJ). Moreover, even though it occurred off-base, the sting targeted military personnel and only incidentally involved a civilian who happened to be at the scene of the sting. And OSI asserted no federal authority to refer the civilian wife for criminal prosecution.

None of these cases endorse an implied exception to the PCA authorizing the military, on a prospective, systematic basis and without coordinating with civilian law enforcement, to pursue, detain, and arrest, off-base, civilians who commit on-base crimes. The OLC asserts, however, that there is a sufficient Defense Department nexus to invoke the military purpose doctrine because there is “a military need to protect the NDAs in their entirety.”

The OLC concedes “that some NDAs consist primarily of vast swaths of unoccupied land with some minimal signage.” It argues, however, that “there is a military necessity to ensure that unauthorized persons are not establishing a position to monitor the activities of U.S. forces for intelligence-gathering purposes or conducting reconnaissance in preparation for a terrorist attack.” And it asserts that the unoccupied land may attract those who want to engage in criminal activity on the base.

These dangers may be well-founded. But it is here that the danger inherent in OLC’s reasoning is most apparent. Arguing that a military installation is too large to administer within existing law to alter the contours of that law puts the Defense Department at the helm in deciding what does and does not constitute a PCA violation. Indeed, the Defense Department’s operational takeover of the southern border reflects a similar, unbounded logic. Statutory law designates Customs and Border Protection as the primary federal agency responsible for security at the nation’s land borders, and 6 U.S.C. § 211 designates the CBP commissioner as responsible for “interdiction of persons and goods illegally entering or exiting the United States.” It further requires that the commissioner “detect, respond to, and interdict terrorists, drug smugglers and traffickers, human smugglers and traffickers” as well as “safeguard the borders of the United States to protect against the entry of dangerous goods.” Nevertheless, the Defense Department now asserts the responsibility to “protect the U.S. southern border from unlawful entry and to maintain the sovereignty, territorial integrity, and security of the United States.” In appending the military purpose doctrine to this transformation of civilian law enforcement into a military mission, the administration crafts its own exception to the PCA.

In this respect, the OLC’s logic is strikingly similar to the now-repudiated articulation of the military purpose doctrine staked out immediately after 9/11. In a 2001 OLC memo, John Yoo argued that “[b]ecause using military to combat terrorist attacks would be for the purpose of protecting the nation’s security, rather than executing the laws, domestic deployment in the current situation would not violate the PCA.” Unlike the OLC’s present memo, Yoo conceded that this approach would make it difficult to distinguish military from civilian law enforcement functions. But he asserted that “courts will defer to the executive branch’s representations.” A 2002 OLC memo used, almost verbatim, the same logic. In 2008, however, the OLC disclaimed these “broad conclusion[s]” as “far too general and divorced from specific facts and circumstances to be useful as an authoritative precedent.”

To this admonition one might add that this logic fundamentally confounds the PCA and is without meaningful limiting principle. OLC’s Aug. 14 opinion gestures towards, and then ignores, this slippery slope. It argues that statutory limits on the establishment of an NDA and any additional limits Congress “may impose” prevent the opinion from giving the military “a free license to enforce civil law.” But these limitations have nothing to say about the opinion’s underlying transformation of a civilian function into a military mission. That move may be performed well beyond the confines of misdemeanor trespass prosecutions at the southern border, and to far more sweeping effect.

*          *          *

OLC’s memo purports to be a straightforward application of statute and long-standing executive and judicial practices to authorize an incremental increase in military authority. It is not. Statutory law does not support its arguments. Existing case law relies on fact patterns that are, in key respects, distinct. And the logic it relies on admits no meaningful limit. In the prosecutions that will inevitably follow, courts should reject these arguments and the dangerous repercussions they entail.