The Trump Defense Department’s First Border Deployment: A Return to the Past

On Jan. 22, Acting Defense Secretary Robert Salesses announced the Defense Department’s first border deployment of the second Trump administration. The deployment is nearly identical to past actions during the first Trump administration, and is largely consistent with the Biden administration’s border deployments as well. Of course, this is only the beginning—and, as I outlined earlier this month in Lawfare, Trump’s executive orders exhibit a willingness to entertain far more extraordinary legal theories and military deployments than exercised here. Nevertheless, it’s noteworthy that this first attempt adheres to past practice rather than attempting to break new ground.

Salesses authorized 1,500 military personnel to support the Department of Homeland Security (DHS) at the southern border. That deployment is on top of the 2,500 military personnel already supporting DHS with border enforcement. These personnel are split among four tasks: providing “real time situational awareness” to Customs and Border Protection (CBP) officers, assisting with logistics, performing aerial surveillance, and undertaking “intelligence analysis.”

All indications suggest that this military support is based on a DHS request for assistance originally transmitted during the Biden administration. First, the range of tasks is identical to what the Biden administration announced as early as 2023. Second, a senior Defense Department official told reporters that only “participation and temporary barrier construction” (which I’ll address in a moment) are new DHS requests.

But two forms of Defense Department support provided here depart from Biden administration practice. First, according to Salesses, the Defense Department is providing “military airlift to support DHS deportation flights.” DHS agents, importantly, are performing all law enforcement functions during these flights—consistent with legal restrictions on the military’s role in carrying out law enforcement under the Posse Comitatus Act. And second, the Defense Department “will begin assisting in the construction of temporary and permanent physical barriers to add additional security to curtail illegal border crossings and illicit trafficking.” A recent Defense Department press release appears to indicate that this includes emplacing concertina wire around the border barrier, a practice that is consistent with what Trump directed in 2019.

The Defense Department confirmed a few other important aspects of this deployment. First, troops are using existing rules for the use of force, notwithstanding a Trump executive order requiring a review of these rules. Second, the Defense Department confirmed that it has not yet received a DHS request to detain migrants on military installations. Third, all the military personnel are active duty (not National Guard personnel or other reservists). And, finally, the Defense Department stated that none of the authorized military tasks included law enforcement activities.

Although the Defense Department didn’t provide the legal basis for these activities, we can readily infer them based on past practice and press releases. The department stated that it was relying on “existing authorities” for this military deployment. As I’ve written previously, the four duties outlined for the additional 1,500 military personnel are easily authorized by provisions of Chapter 15 of Title 10 and Section 1059 of the National Defense Authorization Act for fiscal year 2016. The first authorizes Defense Department support to federal law enforcement agencies. The second more specifically authorizes military deployments in support of CBP to enhance security at the southern border.

The only authority of which I’m aware that authorizes the Defense Department to support DHS with erecting temporary and permanent border barriers is 10 U.S.C. § 284. Section 284 authorizes the Defense Department to support law enforcement agencies with “construction of roads and fences and installation of lighting to block drug smuggling corridors across international boundaries of the United States.” Incidentally, this is one of the authorities the Defense Department relied on to build a border wall during the first Trump administration.

Defense Department airlift support to another federal agency is governed by a Kafkaesque assemblage of statutes and Defense Department regulations. Generally, support provided by one agency to another is governed by the Economy Act (31 U.S.C. § 1535). Such support is, as a rule, provided on a reimbursable basis. This is reinforced in Defense Department Instruction (DoDI) 4500.56, “Use of Government Aircraft and Air Travel.” An exception is provided, however, for Defense Department support of another federal agency when approved by the secretary of defense (see DoDI 4515.13 § 12.3 and DoDI 4500.56). There’s no indication in the Defense Department’s announcement about the precise mechanism by which the department authorized deportation airlift support. But I would not be surprised if Salesses authorized it pursuant to this latter authority.

Salesses ended his public statement by saying that “President Trump directed action from the Department of Defense on securing our nation’s borders and made clear he expects immediate results. That is exactly what our military is doing under his leadership.” Under the legal hood, however, this support does not depart from past practice. And much of it is consistent with the Biden administration’s past use of non-emergency authorities.

But the new administration is less than a week old. Defense Department officials anticipate additional requests for assistance. And it is not yet clear what projects President Trump might personally direct the military to undertake—potentially moving far beyond this well-trodden legal ground.