On April 11, President Donald Trump announced his intention to turn a strip of federal land along the U.S. southern border into a massive “National Defense Area,” effectively creating a new 170-square-mile U.S. military installation. The plan was described in a National Security Presidential Memorandum (NSPM-4), titled “Military Mission for Sealing the Southern Border of the United States and Repelling Invasions.” The document sets in motion the creation of a military area that is twice the size of Washington, D.C. It also expands the U.S. military’s role in stopping migrants crossing the border.
Typically, the establishment of a new military area of this size would require congressional approval. Congress has historically played a critical role in federal land management through its constitutional powers derived from both the Property Clause and the Enclave Clause. But Trump was able to circumvent Congress this time by declaring a national emergency at the southern border, thereby eliminating the statutory requirement for congressional approval. Further, environmental laws have traditionally played an important role in pumping the brakes on federal actions that impact the human environment and endangered species alike (there are 23 federally endangered species at the border). But the Environmental Protection Agency and the Fish and Wildlife Service are actively dismantling regulatory protections found in both the National Environmental Policy Act and the Endangered Species Act. Absent immediate pushback from Congress or a federal court enjoining the transfer of land to the Department of Defense, the creation of this military area appears to be a fait accompli. The result is a significant increase in the military’s mission at the southern border and further obfuscation of the military’s role in domestic law enforcement functions.
NSPM-4 is best read alongside two executive actions issued in January, declaring a national emergency at the southern border and Executive Order 14167, “Clarifying the Military’s Role in Protecting the Territorial Integrity of the United States.” Taken together, these directives seek to accomplish four major objectives, all of which significantly expand the military’s role in border enforcement.
A Transfer of Federal Lands to the Department of Defense
First, Trump is directing the transfer of a 60-foot strip of federal land lying parallel to the U.S.-Mexico border from control of three federal agencies (Interior, Agriculture, and Homeland Security) to the Department of Defense. This land, known as the Roosevelt Reservation, is a noncontiguous strip of federal land that snakes along the southern border from New Mexico to California. President Theodore Roosevelt established the reservation in 1907 to prevent smuggling between the United States and Mexico. In initiating this massive land transfer, Trump highlighted the need for DOD jurisdiction over these lands so that the military could conduct activities such as border-barrier construction and the placement of detection and monitoring equipment.
NSPM-4 calls for a “phased implementation” of this transfer. Initially, only a section of the Roosevelt Reservation in New Mexico, east of Fort Huachuca, will be placed under the DOD’s jurisdiction. But this transfer is only the beginning. NSPM-4 grants what amounts to plenary authority to the secretary of defense to “extend activities under this memorandum to additional Federal lands along the southern border.”
Bypassing Posse Comitatus Act Restrictions
Second, the establishment of a National Defense Area increases the military’s role at the southern border, effectively bypassing longstanding legal restrictions put in place by the Posse Comitatus Act. The Posse Comitatus Act prohibits federal military forces from being used in a law enforcement capacity, such as searching, seizing, detaining, and arresting people entering the country. The Posse Comitatus Act does not apply to National Guard members under state control. Today, there are approximately 10,000 active-duty soldiers operating at the border alongside members of the National Guard. By statute, Congress has granted the military broad authority to protect federal property. Now, federal military forces at the southern border will be empowered to arrest, detain, search, and seize anyone—migrant or otherwise—that attempts to cross into the new National Defense Area.
What’s more, NSPM-4 references myriad statutory authorities—such as the Engle Act (43 U.S.C.-§§ 155-158), Internal Security Act (50 U.S.C. § 797), and 10 U.S.C. § 2672—that reinforce military commanders’ authority to exclude persons from military installations. Indeed, the secretary of defense has the authority under existing law to protect all buildings, grounds, and property under his jurisdiction. In protecting federal property, 10 U.S.C. § 2672 authorizes military officers or agents to enforce federal laws and regulations for the protection of property, and make arrests. And NSPM-4 also highlights a criminal statute, 18 U.S.C. § 1382, that makes it illegal to enter into a “military, naval, or Coast Guard property.”
The authority to prohibit persons from military installations is reinforced in Pentagon regulations that permit direct law enforcement assistance for “actions related to a commander’s inherent authority to maintain law and order on a DOD installation or facility.” An April 16 Pentagon news release reinforced the military’s growing mission in defending the border:
Service members stationed at the border and operating on that land will have greater authority to execute their mission. They will be governed by the same rules as when they are defending any other military installation, such as apprehending trespassers and passing them to appropriate civilian or federal law enforcement officials.
In sum, by transferring federal public lands to the military, Trump is sharply increasing the authority of the military to arrest, detain, search, and seize anyone entering the new property under military authority. The creation of a National Defense Area, in turn, marks an extraordinary shift in the military’s role from indirectly supporting law enforcement to actively serving in a law enforcement capacity. For migrants, the National Defense Area also creates a new offense under the federal criminal code: 18 U.S.C. § 1382 prohibits unlawful entry into any military installation, with a penalty of up to six months in prison.
Muddying the Waters of the Military Purpose Doctrine
Third, NSPM-4 continues the trend of using language that ties immigration flows at the border with broader national security authorities and core military missions. For example, NSPM-4 exclaims that the southern border is “under attack from a variety of threats.” Trump is therefore assigning the military the “mission of repelling the invasion and sealing the United States southern border.” Trump has invoked similar language in invoking the Alien Enemies Act, declaring that the United States is being invaded by a predatory incursion of a transnational gang.
By using such forceful, martial language, Trump is further muddying the already murky waters of the military purpose doctrine, which allows an exception to the Posse Comitatus Act. The military purpose doctrine authorizes “actions taken for the primary purpose of furthering a DOD or foreign affairs function of the United States.” Normal Posse Comitatus Act restrictions do not apply to military activities that further a “military purpose.” Yet deciphering what actions fall within the military purpose doctrine is difficult in ordinary circumstances. Indeed, the Office of Legal Counsel wrote that differentiating between authorized military activities and unauthorized law enforcement functions is “no easy task.” I would characterize NSPM-4 as a continuation of a trend that engages in purposeful ambiguity by employing martial language—“repelling invasions” and “under attack”—that expands the scope of the military purpose doctrine beyond recognition.
A Shortcut to Border Wall Construction Funding
Fourth, the NSPM-4 reference to border-barrier construction is particularly noteworthy. The newly formed National Defense Area bolsters the president’s authority to use military construction money to build the border wall. This military construction authority at 10 U.S.C. § 2808 authorizes military construction projects during time of national emergency “that are necessary to support [] use of the armed forces.”
When Trump sought to employ the same authorities in 2019, he faced legal setbacks when the Ninth Circuit held that the border wall construction was not necessary to “support the use of the armed forces . . . nor were they military construction projects.” By effectively creating a new military installation out of whole cloth, Trump lawyers will argue that, unlike before, the border wall is being constructed on a military facility and amounts to a bona fide military construction project. And “military installation” is broadly defined to encompass established bases as well as “other activity under the jurisdiction of the Secretary of a military department.” To be sure, Congress recently placed a cap on emergency military construction authority—$100 million for construction projects within the United States—but NSPM-4 appears to bolster Trump’s ability to tap into funds set aside for military construction projects.
What are the Possible Checks on this Authority?
Congressional Constitutional Authority. NSPM-4 begins by pointing to Article II commander-in-chief powers that empower the executive branch to protect the homeland and ensure the territorial integrity and sovereignty of the United States. National security powers are famously shared between the executive branch and Congress. Congress, after all, controls the purse strings and has the authority to “raise and support” the Army. Unlike shared national security powers, constitutional authorities over federal property are the exclusive domain of Congress. The Constitution’s Property Clause could not be clearer: Congress has the “Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States.” And under the Enclave Clause, Congress has authority to “exercise exclusive Legislation . . . for the Erection of Forts, Magazines, Arsenals, dock-Yards, and other needful Buildings.”
The Constitution envisions a congressional role in governing all federal property. This clearly encompasses the unilateral transformation of civilian-controlled lands to military-controlled areas. Yet, Congress has been missing in action as of late and appears reluctant to flex its constitutional muscles. Ideally, Congress will reassert its role in federal land management through the National Defense Authorization process. The House and Senate Armed Services Committees will be holding hearings and legislation markup sessions soon on this year’s bill.
Congressional Statutory Authority. Congress has not approved this massive land transfer. Under the Engle Act, approval by Congress is required for withdrawal, reservation, or restriction of over 5,000 acres for any Department of Defense project or facility. But this limitation does not apply today due to Trump’s declaration of a national emergency at the southern border. This is yet another example that showcases the need for reform of the National Emergencies Act, which grants extraordinary power to the president.
Environmental Law Protections. Finally, during the first Trump administration, environmental groups enjoyed considerable success in establishing Article III standing and using both the National Environmental Protection Act and the Endangered Species Act to halt border wall construction and military activities at the border. But the creation of the new National Defense Area—coupled with the concurrent evisceration of environmental regulations—make future environmental challenges far less likely to succeed.
Environmental laws would normally apply to both the land transfer and the border wall construction. After all, the creation of a massive National Defense Area surely constitutes a “major federal action,” that requires an environmental impact statement prepared under the auspices of National Environmental Protection Act. But in a remarkable step that stunned environmentalists, Trump began rescinding all Council on Environmental Quality regulations issued under the law.
Relatedly, the southern border is home to 23 federally endangered species and their critical habitats that normally enjoy robust protections under the Endangered Species Act. The law prohibits the “take” of any endangered species, defined as actions that “harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect.” For decades, harm has been interpreted broadly to prohibit both harm to an endangered species as well as its critical habitat.
Six days after NSPM-4 was issued, the U.S. Fish and Wildlife Service proposed a new rule rescinding the Endangered Species Act’s definition of “harm.” It proposed a definition that only includes an “affirmative act directed immediately against a particular animal,” rather than an act that could indirectly harm an endangered species’ population. Although this new definition is not yet finalized, changing the longstanding definition of harm clears a possible path for border wall construction and military activities that would otherwise be illegal under the Endangered Species Act.
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With just two weeks since NSPM-4 was issued, it is too early to tell if this massive new tract of military land will trigger a congressional response or judicial intervention. Nevertheless, Trump’s efforts to militarize the southern border are on track to be far more successful than they were during his first administration.
Editor’s note: This piece is part of the Collection: Just Security’s Coverage of the Trump Administration’s Executive Actions