Trump Signs NSPM-4 Transferring Roosevelt Reservation to DoD as First 'National Defense Area' at Southern Border; 170-Mile NM Strip Becomes Military Installation Without Congressional Approval

On April 11, 2025, President Donald Trump signed National Security Presidential Memorandum 4 (NSPM-4), titled “Military Mission for Sealing the Southern Border of the United States and Repelling Invasions.” The memorandum transferred jurisdiction of a section of the Roosevelt Reservation in southern New Mexico, east of Fort Huachuca, to the Department of Defense — effectively creating a new 170-mile, ~170-square-mile U.S. military installation along the U.S.-Mexico border without congressional approval typically required for a military area of this scale.

The Roosevelt Reservation is a 60-foot-wide strip of federal land running parallel to the U.S.-Mexico border across California, Arizona, and New Mexico. It was established by President Theodore Roosevelt in 1907 to prevent cross-border smuggling. The reservation does not extend into Texas, where most border land is privately owned. NSPM-4 designates a first section of this strip as a “National Defense Area” (NDA), placing it under DoD jurisdiction and authorizing federal military forces to “arrest, detain, search, and seize” anyone — migrant or otherwise — who enters.

The mechanism creates a new federal criminal exposure: under 18 U.S.C. § 1382 (unlawful entry upon a military installation), trespass on the NDA is punishable by up to six months in prison. For migrants apprehended inside the zone, the trespass charge stacks on top of the existing unlawful-entry charge under 8 U.S.C. § 1325 — producing two federal charges from a single act of border crossing. The Just Security analysis (April 29, 2025) and subsequent ACLU analysis identified this as a structurally novel use of military-installation trespass law against civilians whose conduct would otherwise be prosecuted as a routine immigration violation.

NSPM-4 expressly authorizes the Secretary of Defense to “extend activities under this memorandum to additional Federal lands along the southern border” in coordination with DHS. The authority is delegated open-endedly to the executive branch with no congressional reporting requirement, no acreage cap, and no sunset clause.

The Posse Comitatus question. The Posse Comitatus Act (18 U.S.C. § 1385) prohibits federal military forces from being used in a domestic law-enforcement capacity. NSPM-4 routes around this by reframing the activity as protection of military property rather than civilian law enforcement: the soldiers are not arresting migrants for immigration violations (which would be a Posse Comitatus violation), they are arresting trespassers on a military installation (which is not). The Just Security analysis identifies this as the load-bearing legal-architectural move; the ACLU analysis flags it as “a dangerously overbroad tool” that “effectively bypasses longstanding legal restrictions.”

The administrative-redesignation mechanism. The new criminal exposure is not produced by new conduct, new statute, or new appropriation. It is produced by administrative action — the executive branch redesignating existing federal land as military property. The same act of border crossing that was prosecutable under one statute on April 10, 2025 became prosecutable under two stacked statutes on April 12, 2025, with the only intervening event being the President’s signature on a memorandum. This is the geographic-and-jurisdictional analog of the OCC’s April 1, 2026 amendment to 12 CFR 5.20 (see 2026-04-01–occ-12-cfr-5-20-amendment-trust-bank-chartering-rule-effective): both are instances of administrative-text-change as precondition for the legal consequence that follows.

Subsequent expansion. Per the open-ended Secretary-of-Defense authority in NSPM-4, additional NDA designations followed. Arizona’s NDA was added July 2025 (KJZZ reporting). By April 2026, the ACLU-NM reported total NDA acreage in New Mexico alone had reached 109,651 acres — orders of magnitude beyond the initial 170-square-mile (~108,800-acre) designation; the figure indicates expansion within New Mexico beyond the originally-disclosed zone (see 2026-04-21–aclu-nm-invisible-military-bases-border-report and 2026-05-16–haywood-santa-fe-aclu-invisible-military-bases-coverage).

The prosecutorial result. By May 2026, federal magistrate Judge Gregory Wormuth and other federal judges in southern New Mexico had been “slammed with over 4,600 cases” alleging military-trespass violations; one judge was assigned 400+ cases in less than a month. The bulk of those cases were dismissed at the probable-cause stage — see 2025-05-14–wormuth-federal-trespass-dismissals-probable-cause-nda-architecture and the ACLU-NM April 2026 report. The Department of Justice’s response was to begin charging via criminal information (which bypasses the probable-cause requirement) and to increase prosecutorial staffing in southern New Mexico.

This event is the originating administrative action for a federal architecture that, one year on, has produced thousands of federal criminal cases, transferred ~110,000 acres from civilian to military jurisdiction, and re-opened the Posse Comitatus question at scale — all on the basis of a single presidential memorandum issued without congressional authorization, oversight, or sunset.