No End in Sight for U.S. Military Mission Along the Border

Nearly 11,900 U.S. troops remain stationed along the southern border with Mexico, and there is no defined end point for the mission. As the Trump administration continues to expand the military’s role in domestic border security, questions are mounting over the long-term strategy, the escalating costs, and the impact on military readiness.

The Indefinite Mission

What began as a targeted deployment of 5,200 active-duty troops in October 2018 has ballooned into an open-ended military operation spanning multiple states. According to Al Jazeera, approximately 11,900 U.S. troops — including both active-duty forces and National Guard personnel — are currently stationed along the border. The Pentagon has requested $5 billion in its Fiscal Year 2026 budget for the mission, as reported by Military.com, a staggering increase from the $1 billion estimated for the first eight months of 2025.

The Cost of the Mission

The financial toll of the border deployment has become a central point of contention. Democratic lawmakers, led by Sens. Elizabeth Warren (D-MA) and Mazie Hirono (D-HI), have pressed Defense Secretary Pete Hegseth on the rising costs, noting that some Pentagon expenses for border operations cost “over three times more” than when the Department of Homeland Security performs the same function, according to Federal News Network.

A report released in December 2025 found that the Pentagon had diverted at least $2 billion from barracks repairs, school upgrades for children of service members, and training programs to fund the southern border mission, as Federal News Network reported. The largest share — approximately $1.3 billion — went directly to troop deployment costs.

The cost disparities are stark. Military aircraft used for deportation flights — C-17s costing over $28,000 per flight hour — are more than three times as expensive as the civilian ICE aircraft that typically handle such operations, which cost $8,577 per flight hour. Similarly, the migrant detention facility at Guantanamo Bay costs $272,000 per bed to operate, compared to $57,000 per bed at standard ICE facilities.

Military Zones and Legal Questions

The Trump administration has established multiple “National Defense Areas” along the border, marking a significant expansion of the military’s domestic law enforcement role. These include a 100-kilometer (63-mile) zone in Texas known as the Texas National Defense Area and an 18-meter-wide, 270-kilometer-long strip in New Mexico where troops can temporarily detain migrants.

These zones operate under legal authorities that allow the military to detain individuals without invoking the Insurrection Act of 1807, which requires extraordinary circumstances such as civil disorder. New Mexico Gov. Michelle Lujan Grisham called the military zone in her state “a waste of resources and military personnel, especially when migrant crossings are at the lowest in decades.”

Counter-Drone Gaps: A New Frontier

Perhaps the most urgent operational challenge facing troops at the border is the proliferation of cartel drones. Gen. Gregory M. Guillot, commander of U.S. Northern Command (NORTHCOM), has warned that troops lack portable counter-drone systems for patrols. “The cartels are flying over our soldiers and Marines all the time,” Guillot said at the annual SOF Week conference in Tampa, as reported by Business Insider.

Guillot described the southern border as “a literal and a figurative sandbox” for testing emerging counter-drone technologies. “If you’re willing to bring it down to the southern border, we’ll put it to use. We’ll tell you if it works,” he said. The military now has “hundreds of systems” operating along the border as officials try to identify technologies capable of protecting troops from unmanned aerial vehicle (UAV) threats.

Adm. Frank Bradley, who leads U.S. Special Operations Command, warned that the “democratization of technology” has made lethal drone capabilities accessible to non-state actors. “The barrier to be able to have a lethal, precise weapon to aim and orient at our maneuvering forces is lower to the point where anyone with an Alibaba or an Amazon account can piece those things together,” Bradley said.

Readiness Concerns

A central tension in the border mission is the trade-off between domestic security and military readiness. Retired Gen. Daniel Hokanson, former National Guard Bureau Chief, stated bluntly: “There is no military training value for what we do” on border missions.

Lawmakers have warned that deployment-ready units are being diverted from their core warfighting missions. The 10th Mountain Division — recently trained and certified for large-scale combat operations — was sent to the border in early 2025, followed by the 101st Airborne Division, the Army’s only air assault division. Critics argue this undermines the military’s ability to respond to genuine national security threats abroad.

Defense Secretary Pete Hegseth has defended the mission, arguing that “border security is national security.” During his first town hall for DoD personnel, Hegseth said NORTHCOM has done an “amazing job” planning for a long-term defensive strategy in the region.

A Historical Perspective

The use of active-duty military personnel at the southern border is not new, but it has expanded dramatically under the Trump administration. Under the Posse Comitatus Act of 1878, the U.S. military is generally prohibited from engaging in law enforcement activities on domestic soil. However, presidents have used various legal authorities — including the National Emergencies Act and the creation of National Defense Areas — to deploy troops in support roles.

President Trump’s January 2025 executive order directing NORTHCOM to “seal the borders” marked a significant escalation. Since then, the administration has expanded the military footprint, created military zones where troops can detain migrants, used military aircraft for deportation flights, and expanded the migrant detention facility at Guantanamo Bay.

What’s Next

The border mission shows no signs of winding down. With $5 billion budgeted for FY2026 and the Pentagon betting on a Trump agenda bill to backfill diverted funds, the financial commitment is only expected to grow. The counter-drone technology gap will likely be addressed through accelerated testing and procurement, with the border serving as a proving ground for systems that may later be deployed in combat zones overseas.

However, the broader questions remain unanswered. What is the administration’s exit strategy? How will the indefinite deployment affect the military’s ability to respond to crises abroad — particularly as units like the 10th Mountain Division and 101st Airborne are cycled through border duty instead of traditional training? And what precedent does this set for the role of the U.S. military in domestic affairs, especially as National Defense Areas effectively allow troops to perform law enforcement functions that have been off-limits since the Posse Comitatus Act of 1878?

As migrant crossings have fallen to their lowest levels in decades, the continued presence of nearly 12,000 troops at the border raises a fundamental question about the purpose and endpoint of America’s largest domestic military operation. For now, the answer from the administration appears to be: there is none.