Published by The Lawfare Institute
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In recent weeks, the prospect that President Trump might declare a national emergency in order to fund the construction of a wall along the U.S.-Mexico border has triggered new concerns regarding his administration’s commitment to the rule of law. Some commentators have even suggested that the president’s invocation of new, unprecedented emergency authorities could amount to a constitutional crisis. But for all the valid concerns such actions might raise, the discussion surrounding it risks overshadowing serious constitutional questions already raised by his administration’s actions at the border—questions that have nothing to do with any wall.
For almost three months, thousands of active duty U.S. military personnel—not the national guardsmen used in prior border deployments—have taken up temporary residence on the southern border. At times operating in full battledress, they have provided Customs and Border Protection (CBP) personnel with a diverse array of assistance, ranging from transportation and medical services to the deployment of concertina wire. Premised on the purported threat posed by large caravans of Central American migrants attempting to enter the United States, the deployment of these personnel was recently extended through September 2019. Until then, these troops will continue to operate at the intersection of military operations and civilian law enforcement efforts—two domains that the U.S. legal system has traditionally tried to keep separate.
Whatever policy concerns these military personnel may raise, most of their activities fit comfortably within existing statutory authorizations and therefore do not raise serious legal concerns. An important exception, however, are the “military protective activities” that Trump authorized on Nov. 20, which permit deployed servicemembers to use force if necessary to defend CBP personnel from the purported threats posed by the migrant caravans. Drafted to resemble certain practices set out in existing military guidelines, authorization of the deployment of military personnel for this purpose is a novel step that may reflect a new assertion of legal authority by the president. The Trump administration, however, has resisted providing the public with a legal justification for these activities. As a result, the full scope of this assertion—and its implications for the future scope of presidential authority—remains unclear.
Assisting Law Enforcement and Posse Comitatus
Since 1878, Congress has made it a crime to intentionally use members of the Army (and later the Air Force) for the purposes of posse comitatus—a Latin phrase describing the enlistment of civilians to assist in law enforcement tasks—or to “otherwise ... execute the laws,” except where expressly authorized by Congress or the Constitution. Defense Department policies extend this same basic limitation to the Navy and Marine Corps but allow for certain case-by-case exceptions. National Guard personnel, however, are not subject to this restriction when they are acting pursuant to the authority of individual state governors—a fact that likely explains the central role such forces have played in prior border deployments.
The Justice Department maintains that the primary purpose of the posse comitatus restriction is to “prohibit military personnel from directly coercing, threatening to coerce, or otherwise regulating civilians in the execution of criminal or civil laws.” Under relevant case law, efforts at civilian law enforcement generally violate this restriction where they make “direct active use” of military personnel, are “pervade[d]” by military involvement, or use military power to subject civilians to measures that are “regulatory, proscriptive or compulsory in nature.” That said, this restriction does not reach activities that military personnel pursue for military or other non-law enforcement purposes, even if those activities incidentally benefit civilian law enforcement. Hence, the posse comitatus restriction does not prohibit security measures on military bases, the off-base investigation of servicemember conduct or even duly authorized military operations within the United States, provided they are all pursued for independent military purposes.
Congress has expressly authorized the military to provide various forms of assistance for civilian law enforcement efforts since 1981, thereby exempting these activities from the posse comitatus restriction. Authorized forms of assistance include providing civilian law enforcement agencies with relevant military information, the use of military equipment and facilities, and training and advice. Subsequent legislation has authorized additional forms of support for civilian agencies combating narcotics trafficking and other forms of transnational organized crime, including by transporting non-military personnel, establishing bases of operation and constructing roads and fences along the border.
Together, these provisions readily authorize most of the activities that the military is currently undertaking on the U.S.-Mexico border. But these authorizations are not without limits. Such activities cannot adversely affect military preparedness, a requirement that Congress has tasked the secretary of defense with enforcing. And the costs of most such assistance must be reimbursed unless the secretary of defense issues a waiver on the grounds that the assistance provides military personnel with benefits similar to that of training. (Notably, former Defense Secretary James Mattis repeatedly described the border operation as “great training,” which may be a sign that he supported such a waiver.)
The most important limitation, however, prohibits military personnel acting under these various assistance authorities from “direct participation” in any “search, seizure, arrest, or other similar activity” unless otherwise authorized by law. As the Justice Department explained in a 1991 Office of Legal Counsel opinion, this restriction was intended to make clear that Congress was not authorizing any “direct, physical confrontation between military personnel and civilians” for civilian law enforcement purposes—something that Congress understood to be prohibited by the posse comitatus restriction and which would, in the words of the House report on the 1981 legislation, “fundamentally alter the nature of the relationship between the military and civilian society.” Instead, such activities remain prohibited, unless and until Congress separately authorizes them.
The Problem with “Military Protective Activities”
This became a point of concern on Nov. 20, when the president issued a decision memorandum that expanded the military mission at the border. Citing “credible evidence and intelligence indicat[ing] that migrant caravans ... may prompt incidents of violence and disorder” that could threaten CBP personnel and “prevent them from performing the Federal functions necessary to secure and protect the integrity of the southern border,” he directed the secretary of defense to “deploy appropriate numbers of units and personnel” to perform “military protective activities that are reasonably necessary to ensure the protection and safety” of CBP and other federal personnel. Such activities were defined to include “a show or use of force (including lethal force, where necessary), crowd control, temporary detention, and cursory search.”
Both the president’s decision memorandum and the “cabinet order” that accompanied it are careful to distinguish these activities from “traditional law enforcement activities, such as arrest, search, and seizure in connection with the enforcement of the laws,” which they explicitly do not authorize. Yet they clearly set the stage for “direct, physical confrontation between military personnel and civilians” for the stated purpose of facilitating the CBP’s ability to execute its “Federal functions” at the border—which statute defines as being primarily civilian law enforcement. In this sense, Trump’s Nov. 20 decision appears to be in clear tension with the posse comitatus restriction, which is not limited to direct participation in “traditional law enforcement activities.” And neither the decision memorandum nor the cabinet order provide any guidance on how the president’s order and the law should be reconciled.
The administration could be relying on some statutory exception to the posse comitatus restriction in order to authorize these activities. But the only relevant exceptions are part of the Insurrection Act, which Trump does not appear to have invoked. Last used during the 1991 Los Angeles riots, these exceptions permit the president to deploy the military to enforce the law and preserve federal authority in circumstances of extreme domestic unrest. The most relevant provision specifically authorizes the president to deploy the military “[w]henever [he] considers that unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States, make it impracticable to enforce the laws of the United States ... by the ordinary course of judicial proceedings.” Such circumstances certainly resemble Trump’s rhetoric on the threat posed by the migrant caravan, though there are good reasons to doubt its accuracy. The executive branch, however, has traditionally required “an actual obstruction ... or ... breakdown” before invoking this provision, not the mere threat of such a crisis. And a related statutory provision requires that the president issue a public proclamation whenever he does so, a step Trump has not yet taken.
Alternatively, the Trump administration might be relying on certain exceptions to the posse comitatus restriction recognized by relevant Defense Department manuals and instructions. Each implicitly rests on an assertion of constitutional authority to take otherwise prohibited actions or contends that such actions serve purposes other than civilian law enforcement and thus fall outside the statutory scope of the posse comitatus restriction. Two existing exceptions closely resemble the military protective activities that Trump has authorized but are subject to limitations that exclude such conduct. A third cannot be ruled out entirely but is an odd fit for what precisely the president has authorized.
One exception permits military personnel who are supporting civilian agencies to threaten and use force “in self-defense; in defense of other [Defense Department] persons in the vicinity; or in defense of non-[Defense Department] persons, including civilian law enforcement personnel, in the vicinity when directly related to an assigned activity or mission.” This has obvious parallels to the “military protective activities” authorized by the Nov. 20 memorandum. Yet the requirement that non-Defense Department persons must be “in the vicinity” and “directly related to an assigned activity or mission” to be defended makes clear that this exception is intended to address exigencies in which military personnel find themselves and those near them unexpectedly under threat, similar to the principles of self-defense applied in U.S. rules of engagement. Military personnel deployed to the border for the specific purpose of providing such defense thus appear to be well outside the scope of this exception.
Another exception permits military personnel to exercise what the Defense Department calls “emergency authority” in order to “quell large-scale, unexpected civil disturbances” for the purposes of “prevent[ing] significant loss of life or wanton destruction of property” or “protect[ing] ... Federal property or functions.” This emphasis on protecting “Federal functions” resembles the stated purpose for which the president authorized military protective services at the border. Yet military personnel may only invoke this exception “where prior authorization by the President is impossible,” conditions clearly not applicable to the president’s Nov. 20 memorandum, which provides such authorization. Absent such exigent circumstances, current Defense Department regulations indicate that military personnel may only take such actions where “specifically authorized by the President in accordance with applicable law (e.g., [the Insurrection Act]),” conditions that are clearly not applicable to the president’s Nov. 20 memorandum.
Finally, Defense Department guidelines also recognize an exception for activities “undertaken primarily for a military or foreign affairs purpose,” even if those activities might incidentally benefit civilian law enforcement. The most significant example is “homeland defense,” which relevant Defense Department guidelines identify as a “constitutional exception” to posse comitatus restrictions—one rooted in the president’s Article II authority over foreign affairs and as commander in chief. Trump has certainly described the migrant caravan in national security terms, going so far as to compare it to an “invasion.” But the president has not gone so far as to claim that he can use the same authorities to address the migrant caravan as he can an enemy military force or terrorist group—a claim that would likely prove highly controversial. Moreover, this exception generally requires that a mission have a “legitimate, independent military purpose” for such activities. Yet the stated purpose of the Nov. 20 order is to ensure that CBP can continue to perform its civilian law enforcement role. And if securing the border was a homeland defense mission, then military personnel could be deployed to engage the migrant caravans directly; instead, they are merely tasked with defending the CBP. Hence, while this exception cannot be ruled out, it is at best a poor fit.
What does this all mean? The president’s Nov. 20 memorandum does not fit with what is known about the existing law and policies surrounding the posse comitatus restriction. As a result, the Trump administration appears to be relying on something we don’t know: a new legal argument as to when and why the president may employ military personnel in support of civilian law enforcement efforts.
New Constitutional Territory?
To date, the Trump administration has declined to provide a public explanation of the legal basis for its Nov. 20 memorandum. As a result, one can only speculate as to what this new argument may be. The possibilities range from narrow statutory and regulatory arguments to broad claims of constitutional authority. All have the potential to raise serious concerns, and for that reason warrant greater scrutiny.
The Trump administration may simply be relying on some unannounced shift in executive branch regulations or statutory interpretations. For example, if the military protective activities are only being provided by Navy and Marine Corps personnel, then it may have created a new exception to the Defense Department policies applying posse comitatus restrictions to those armed services. Or Trump administration lawyers may have adopted a narrower reading of the posse comitatus restriction than the Justice Department has traditionally maintained. By narrowing the posse comitatus restriction, either approach could be cause for concern among those who support a sharp civilian-military divide. That said, the implications of such a shift are likely to be narrower and more readily subject to correction by Congress than some of the other arguments the Trump administration could be making.
Another possibility is that the president is relying on a new assertion of constitutional authority. Certainly, the similarities in scope and purpose between the president’s Nov. 20 order and the self-defense and emergency authority exceptions already recognized in Defense Department guidelines suggest that this might be what is happening. Both exceptions implicitly rely on what scholar William Banks has described as “a species of [the president’s] defensive war powers” as commander in chief under the constitution, one that allows him to “repel an attack on the United States or its personnel.” The Trump administration could in turn view the president’s Nov. 20 order as another expression of this same constitutional authority.
Yet this could prove to be a very troubling precedent. Both existing exceptions in Defense Department guidelines are limited to circumstances of extreme exigency, where attempting to comply with otherwise applicable legal requirements would be impossible or at least extremely dangerous. Setting this authority loose from such bounds could set the stage for a major shift in civil-military relations. After all, if the president can deploy military personnel to defend CBP personnel while acting in the course of their duties, why can he not assign armed servicemembers to accompany FBI agents when executing search warrants? Or station them at post offices in high-crime neighborhoods? Perhaps the Trump administration has limiting principles in its legal theory that would prevent such ramifications, but if so, it has not shared them.
Alternatively, the Trump administration may argue that the military protective activities the president has authorized are in fact part of a homeland defense mission, one which he has the constitutional authority to pursue under his war powers. This argument could fit within the military purpose exception described in Defense Department guidelines, albeit awkwardly. Yet it would also raise serious constitutional concerns. The president’s authority to deploy military personnel without congressional authorization overseas is already the subject of substantial debate, and the executive branch’s arguments in support of his ability to do so rely heavily on the president’s authority over U.S. foreign relations. The border deployment, however, is clearly closer to the domestic realm, where the president’s relative constitutional authority relative to Congress is far weaker. Hence, his ability to take such action unilaterally, let alone in direct contradiction of statutory restrictions like the posse comitatus restriction, is even more in question.
Indeed, both constitutional arguments are likely to be complicated by a need for exclusivity. The Nov. 20 memorandum’s clear statement that its purpose is to facilitate the CBP’s federal functions (i.e., civilian law enforcement) makes it difficult to argue that it has some independent purpose that places it outside the statutory scope of the posse comitatus restriction. Instead, the president will most likely have to argue that he has the constitutional authority to act in spite of the legislative restrictions that Congress has put in place. Yet the president’s authority is considered to be at its “lowest ebb” when he acts contrary to Congress, meaning that his actions can only be upheld if they are premised on a “conclusive and preclusive” presidential authority that is not subject to congressional limitation or regulation. This sets an extremely high bar for success, particularly as the text of the Constitution does not favor such a reading. After all, it gives Congress, not the president, the authority to “provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions”—a factor that weighs in favor of Congress’s ability to regulate the domestic use of the military, even if this authority does not directly apply to standing military forces.
Nor is the border deployment likely to escape legal scrutiny indefinitely. While the federal government has never pursued a prosecution under the posse comitatus statute, violations of the restriction have at times provided a basis for excluding evidence, contesting jurisdiction and even civil liability. At least some individuals subjected to law enforcement activities by the CBP at the southern border are likely to find themselves in a position to advance such claims, which will in turn subject the military protective activities at issue to judicial scrutiny. Federal judges may be hesitant to intervene, given the political controversy surrounding the matter and its nexus with national security. But the Supreme Court has described the type of question it raises—whether a statute should be enforced in the face of a contrary claim of presidential authority—as being “emphatically the province and duty of the judicial department” to address, meaning that some court is likely to answer the call at some point.
Thus far, the Defense Department’s strategy for managing concerns over the Nov. 20 memorandum has been to downplay the possibility that it will ever be acted upon. At least this was the approach taken by former Secretary of Defense James Mattis, who asserted that no armed servicemembers were engaged in the activities described in the memorandum and implored reporters: “Relax. Don’t worry about it.” Whether his successors will adopt the same tack is unclear. Regardless, while this may limit the immediate consequences of the president’s decision, it does not address the legal precedent that’s been set—or the actions that the administration’s legal theory may be used to justify in the future.
For this reason, the Trump administration should be made to disclose the legal basis for the Nov. 20 decision memorandum. Public scrutiny will allow legal experts to weigh the argument’s merits and analyze its consequences. Congress and the voting public can then respond accordingly. And if the Trump administration continues to resist such transparency, then Congress should use its oversight authorities to force disclosure. Absent such efforts, this theory is likely to remain hidden from sight. And when it eventually resurfaces, it may do so in ways that are far more troubling.
The author would like to thank Mark Nevitt for his expert advice in drafting this piece.