Justice Department expands military's power to detain migrants near border

The Justice Department has expanded the military's power to detain migrants near the U.S.-Mexico border, according to a legal opinion issued on Friday. This expansion concerns designated "National Defense Areas" along the southern border, which the Department of Defense has set up to deter illegal immigration. While the military generally cannot enforce domestic laws under the Posse Comitatus Act, these zones allow soldiers to detain migrants accused of trespassing, as long as they leave the area before they can be apprehended.

Deputy Assistant Attorney General William Hyde stated that the use of military personnel to arrest trespassers outside these areas does not violate the Posse Comitatus Act, provided there is express statutory authorization and the military's traditional protective power is involved. The Trump administration has established six such zones so far, with six more potentially under consideration.

These areas, which may not appear as military bases, are marked with signs warning against unauthorized entry. Since April 2025, the Justice Department has charged hundreds of individuals arrested in these zones for trespassing, mainly for violating military security regulations or entering restricted military property, which are considered misdemeanors.

Other charges may include crossing the border illegally. While the advisory opinion does not establish legal precedent, it clarifies the military's role in border security under the current administration. The Pentagon has deployed over 20,000 service members to the border since President Trump's second term began, and the Justice Department has charged more than 300 people since April 2025, with charges often linked to both trespassing and border crossing violations.

This move has contributed to a significant decrease in illegal crossings along the southern border, with Border Patrol reporting fewer than 240,000 apprehensions in fiscal year 2025, a sharp decline from previous years.