Pull to refresh
Logo
Daily Brief
Following Why Sign Up
Trump turns the southern border into military ground

Trump turns the southern border into military ground

Force in Play

National Defense Areas let troops detain migrants as trespassers, pushing the edge of Posse Comitatus

December 11th, 2025: Congress clashes over military immigration enforcement

Overview

Updated May 11

Donald Trump has quietly turned long stretches of the southern border into de facto military bases. Under a new system of National Defense Areas, soldiers can stop migrants, hold them, and help prosecutors charge them as trespassers on military land.

California is now pulled into the experiment. A fresh 760-acre militarized zone along the border with Mexico extends a strategy already rolled out in New Mexico, Texas, and Arizona.

A federal judge slapped down Trump's use of troops in Los Angeles. At stake is where the line really sits between border security and martial law at home.

Questions about this story

Free account needed to ask — your question is kept and asked for you right after sign-up. Answers are public.

No questions yet — be the first to ask.

Key Indicators

5
National Defense Areas on the southern border
By December 2025, New Mexico, Texas, Arizona, and now California host militarized zones.
7,000+
Active-duty troops deployed on the border
Soldiers, helicopters, and drones now anchor day‑to‑day enforcement along key stretches.
1,400+
Migrants charged with NDA trespass
New criminal counts layer military trespass onto traditional immigration charges.
Lowest since 1960s
Border Patrol arrest pace
Border crossings are down even as Trump dramatically escalates military involvement.

Voices

Curated perspectives — historical figures and your fellow readers.

Ever wondered what historical figures would say about today's headlines?

Sign up to generate historical perspectives on this story.

Log in Sign Up

People Involved

Donald Trump
Donald Trump
President of the United States
Driving aggressive military-led immigration crackdown
 Doug Burgum
Doug Burgum
Secretary of the Interior
Overseeing transfer of public lands into border military zones
 Pete Hegseth
Pete Hegseth
Secretary of Defense
Implementing and defending military-led border enforcement
 Gavin Newsom
Gavin Newsom
Governor of California
Leading legal and political resistance to Trump’s militarization
 Charles R. Breyer
Charles R. Breyer
U.S. District Judge for the Northern District of California
Ordered Trump to end federalized Guard deployment in Los Angeles
 Gregory B. Wormuth
Gregory B. Wormuth
U.S. District Judge in New Mexico
Questioning and partially curbing NDA trespass prosecutions
 Kristi Noem
Kristi Noem
Secretary of Homeland Security
Defending harsh immigration tactics and military-heavy enforcement

Organizations Involved

U.S. Department of Defense
U.S. Department of Defense
Federal Agency
Operating National Defense Areas and deploying troops on the border

The Pentagon is running a new network of border military zones where troops can detain migrants.
U.S. Department of the Interior
U.S. Department of the Interior
Federal agency
Transferring public lands for use as National Defense Areas

Interior is handing chunks of public land to the military to close so-called border “gaps.”
U.S. Department of Homeland Security (DHS)
U.S. Department of Homeland Security (DHS)
Federal Agency
Partnering with military inside National Defense Areas

DHS runs immigration enforcement inside and alongside the new military zones.
State of California
State of California
State Government
Challenging Trump’s domestic military deployments while hosting new NDA

California is ground zero for both a new border military zone and a fight over martial law.

Timeline

January 2025 December 2025

12 events Latest: December 11th, 2025 · 9 months ago Showing 8 of 12
Tap a bar to jump to that date

  1. Congress clashes over military immigration enforcement

    Latest Oversight

    Lawmakers grill DHS and Pentagon leaders on Guard deployments, NDAs, and Trump’s broader immigration crackdown.

  2. California border lands handed to Navy for new NDA

    Implementation

    Interior transfers about 760 acres from the Arizona line to Otay Mountain to establish a California National Defense Area.

  3. Judge orders end to Trump’s National Guard mission in Los Angeles

    Legal

    Judge Charles Breyer rules Trump overstepped by federalizing California Guard troops to police immigration protests.

  4. ACLU warns NDAs blur line between army and police

    Advocacy

    A detailed report says vast public lands are now treated as military bases, endangering border communities.

  5. Fourth NDA announced in Arizona desert

    Implementation

    The Pentagon unveils a Navy-controlled National Defense Area near Arizona’s Barry M. Goldwater Range.

  6. Military zone stretched to Texas’s southern tip

    Implementation

    An Air Force–run NDA along the Rio Grande makes Brownsville and McAllen neighbors to a military strip.

  7. Judge throws out first wave of NDA trespass cases

    Legal

    A New Mexico judge dismisses charges against about 100 migrants, questioning the new military trespass theory.

  8. Second NDA erected near El Paso, Texas

    Implementation

    A Fort Bliss–linked National Defense Area covers about 63 miles of the West Texas border.

  9. First National Defense Area declared in New Mexico

    Implementation

    Army designates a 170‑mile New Mexico strip as a National Defense Area tied to Fort Huachuca.

  10. Trump orders Pentagon to seize border lands

    Policy

    A national security memo directs DoD to accept jurisdiction over 170 square miles along New Mexico’s border.

  11. Plan surfaces to turn border strip into military “buffer zone”

    Leak

    Reports reveal White House talks to give Pentagon control of a border buffer zone in New Mexico.

  12. Trump labels migration an “invasion” on Day One

    Policy

    Executive Order 14159 brands unlawful migration an invasion and promises sweeping crackdowns.

Scenarios

1

Courts Rein In Trump’s Border Military Experiment

Possible

Discussed by: Brennan Center, ACLU, legal scholars, Senate Democrats, major national newspapers

The immediate trigger would be a decisive appellate ruling that NDA trespass prosecutions violate due process or stretch military authority beyond what Congress allows, combined with Supreme Court skepticism about using emergency powers to militarize domestic law enforcement. If judges like Breyer and Wormuth are upheld, the administration could be forced to narrow NDAs to true base perimeters, stop using troops as first‑line border cops, and drop thousands of pending trespass cases. The zones might survive on paper but lose their teeth as a tool of mass immigration enforcement.

2

National Defense Areas Become a Permanent Border Regime

Likely

Discussed by: Trump officials, border hawks, some conservative think tanks and media outlets

If courts mostly defer and Congress deadlocks, NDAs could quietly become the new normal. Trespass charges would be refined, not abandoned, and the Pentagon would keep expanding zones until nearly the entire land border sits inside some form of restricted military strip. Future administrations, even if less aggressive than Trump, might find it easier to inherit the apparatus than dismantle it. The result: a semi-permanent military footprint at the border, normalized joint patrols, and a generation that grows up assuming soldiers, not just Border Patrol, belong in immigration enforcement.

3

Backlash Forces Congress to Draw a New Line on Posse Comitatus

Possible

Discussed by: Civil-liberties groups, some centrist lawmakers, institutionalist Republicans and Democrats

Sustained public outrage over stories of citizens and migrants prosecuted for wandering into barely marked military zones, combined with governors’ anger at federalized Guard deployments, could push Congress to act. Lawmakers might tighten the Posse Comitatus Act or pass a new statute limiting when and how the military can support immigration enforcement, perhaps banning direct contact between troops and civilians and requiring explicit authorization for NDAs. This scenario doesn’t erase Trump’s changes overnight, but it hardens legal guardrails and deters future presidents from using the same playbook.

4

Military Role Expands from the Border into Interior Cities

Unlikely

Discussed by: Worst-case analyses by civil-liberties advocates and some constitutional scholars

In this darker trajectory, the relative success of NDAs at the border emboldens the White House to push further, citing crime or unrest to justify more frequent federalization of National Guard units and even active-duty deployments inside cities. NDAs become precedent for treating parts of the interior—around ports, rail yards, or migrant shelters—as quasi-military zones. Legal challenges lag behind events, and Congress remains paralyzed. While still constrained by resource limits and public opinion, the practical distinction between domestic policing and military operations begins to erode in everyday life.

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

1877–Early 20th Century

The Posse Comitatus Act After Reconstruction

After federal troops were withdrawn from the South, Congress passed the Posse Comitatus Act, sharply limiting the Army’s role in domestic law enforcement. The law reflected deep suspicion of standing armies policing citizens, shaped by abuse of military power during Reconstruction and earlier conflicts.

Then

The Act curtailed routine use of federal troops against civilians, forcing presidents to rely on narrow exceptions like the Insurrection Act.

Now

For nearly 150 years, it has been the main legal bulwark against using the military as a national police force.

Why this matters now

Current fights over National Defense Areas and federalized Guard units are essentially a live test of whether Posse Comitatus still has teeth in the age of permanent emergencies.

1910–1917

Border Militarization During the Mexican Revolution

As the Mexican Revolution spilled north, the United States stationed tens of thousands of troops along the border and launched the Punitive Expedition after Pancho Villa’s raid on Columbus, New Mexico. The line between external defense and domestic control blurred as soldiers patrolled U.S. towns and rural communities.

Then

The buildup deterred further large-scale raids but fueled tension with Mexico and anxiety among border residents.

Now

It left a legacy of viewing the border as a militarized frontier rather than a civilian law-enforcement zone.

Why this matters now

Today’s NDAs revive that older vision of the border as a military frontier, but this time woven into ordinary immigration policy rather than a discrete cross-border conflict.

2006–2008

Operation Jump Start: National Guard on the Border

Under President George W. Bush, up to 6,000 National Guard troops were deployed along the U.S.-Mexico border to support Border Patrol with surveillance, construction, and logistics. Troops were explicitly barred from making arrests, and the mission wound down after two years amid questions about cost and effectiveness.

Then

The operation temporarily boosted surveillance and barrier construction but had modest impact on long-term migration patterns.

Now

It set a precedent for using Guard troops at the border, but always in a support role, reinforcing the norm against direct military law enforcement that Trump is now testing.

Why this matters now

Jump Start shows how previous administrations kept the military at arm’s length from actual immigration policing, highlighting how radical it is to let troops detain migrants as trespassers.

Sources

(16)
+10
Associated Press The Washington Post U.S. Department of the Interior E&E News / Politico U.S. Department of Defense Wikipedia Stars and Stripes UPI ACLU Brennan Center for Justice Reuters Wall Street Journal U.S. Senate Office of the Governor of California Associated Press The Washington Post