Why It Matters

The Department of Defense (DoD) has obligated nearly $2.64 billion for southern border security operations since the start of fiscal year 2025, according to a Government Accountability Office (GAO) report released this month.

The scale of DoD border security funding reflects a significant shift in policy. Millions of people enter the U.S. along its nearly 2,000-mile-long border with Mexico each year, and the southern border has long been vulnerable to illegal activities such as drug smuggling and organized crime. But the Pentagon's direct operational involvement at this scale is relatively new. In January 2025, the President directed the Department of Defense to help the Department of Homeland Security (DHS) gain complete operational control of the border, triggering a cascade of financial commitments that have only begun to come into focus.

The GAO report published July 13 examines how DoD has managed these costs and whether the department has adequate systems to track spending and ensure accountability.

The Big Picture

The Department of Defense employed five distinct funding strategies to support southern border operations since the start of fiscal year 2025, according to the GAO report. This multipronged approach reflects the ad hoc nature of the Pentagon's initial response to the presidential directive.

The largest single move was a realignment of $1.74 billion in funding from amounts appropriated for fiscal year 2025 from various funding categories. This represented existing money that DoD shifted from its original purpose to border operations. The department also transferred $608 million from DoD's Drug Interdiction and Counter-Drug Activities, Defense account, tapping into a longstanding pot of money designated for counternarcotics work.

A third strategy involved military construction authorities. DoD used $300 million from within existing military construction appropriation accounts to fund border barrier projects. This approach allowed the Pentagon to bypass some traditional procurement processes by relying on construction authorities already embedded in the defense budget.

The fourth major funding source was new appropriations. DoD began obligating amounts from $1 billion appropriated in Public Law 119-21, commonly known as the One Big Beautiful Bill Act. This legislation provided fresh money specifically intended for border operations.

Finally, DoD began providing some support to DHS in fiscal year 2026 that is eligible for reimbursement, creating a fifth funding mechanism that shifts some costs to the Department of Homeland Security.

As of March 31, 2026, DoD reported obligating $2.64 billion for southern border operations since the start of fiscal year 2025. Of that total, $305 million is reported as eligible for reimbursement by the Department of Homeland Security, meaning the actual net cost to DoD may be somewhat lower, though reimbursement depends on DHS's ability and willingness to pay.

What DoD Border Operations Include

The Pentagon's border security mission encompasses multiple distinct activities. DoD-directed activities include securing DoD-administered lands along the border known as National Defense Areas. The department is also constructing permanent border barriers as part of its southern border operations. Additionally, DoD is providing support to DHS in response to requests for assistance, ranging from logistics to personnel deployment.

The diversity of these activities means that the $2.64 billion figure encompasses everything from concrete and steel for physical barriers to personnel costs, transportation, and equipment. The GAO report does not break down spending by activity type, making it difficult for outside observers to assess whether particular expenditures represent good value or redundancy with existing DHS efforts.

The Tracking Problem

A central finding of the GAO report is that DoD has only recently established systems to track southern border costs with any rigor. The Office of the Under Secretary of Defense (OUSD) and the military services established a process for tracking southern border costs, but this infrastructure was built in response to the January 2025 presidential directive, not in anticipation of it.

DoD issued guidance and business rules for pulling data from the military services' financial ledgers into Advancing Analytics, DoD's enterprise-level management system used for reporting. However, this represents a makeshift solution to an unprecedented demand for cost tracking.

More concerning is what remains unfinished. OUSD officials stated they are working to finalize standard operating procedures (SOPs) that would codify DoD's process to manage and execute costs of southern border operations and provide continuity in the event of personnel turnover. In other words, the current tracking system depends heavily on individual officials and informal processes rather than institutionalized procedures. If key personnel leave, institutional knowledge could walk out the door with them.

What Comes Next

The GAO report provides Congress with the baseline data it needs to conduct more detailed oversight of DoD border security funding. With nearly $2.64 billion already obligated and the policy still in early stages, the Pentagon's border role will likely remain a focus of legislative scrutiny. The unfinished standard operating procedures represent a particular vulnerability: if Congress or future administrations want to wind down or significantly alter the military's border mission, the lack of institutionalized processes could complicate that transition.

Whether that reorientation proves sustainable, cost-effective, or appropriate remains an open question that policymakers will need to grapple with in the months ahead.

The Bottom Line

The GAO was asked to review DoD's costs to support operations at the southern border following a directive from Congress. Senate Report 119-39, accompanying a bill for the National Defense Authorization Act for fiscal year 2026, includes a provision directing GAO to examine DoD's southern border costs. This reflected bipartisan concern on Capitol Hill about the scale and management of the Pentagon's new border mission.

The GAO report, which spans 35 pages, did not include formal recommendations. Instead, the document serves primarily as a factual accounting of how much money DoD has obligated and what systems the department has put in place to track those expenditures. DoD provided technical comments only (no official comments) on the report, suggesting the Pentagon did not dispute the GAO's findings but also did not offer a broader defense of its approach.

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