The Justice Department on Friday issued a legal opinion giving the U.S. military broader powers to detain migrants accused of trespassing in areas that the Department of Defense controls as part of President Trump's crackdown at the southern border.

     The opinion from the Justice Department's Office of Legal Counsel concerns large swaths of land near the U.S.-Mexico border that the second Trump administration has designated as "National Defense Areas" for the purposes of deterring illegal immigration.  As they should.

     While the military is generally prohibited from enforcing laws on domestic soil under the longstanding Posse Comitatus Act, the zones have allowed soldiers to detain migrants accused of entering the national defense areas, which are closed to civilians. The arrangement has allowed the Justice Department to prosecute those arrested in the zones for trespassing on military land.

      In its opinion, the Justice Department said military personnel can arrest individuals who leave national defense areas before they can be apprehended for trespassing. "In sum, we conclude that the use of military personnel to arrest trespassers just outside of an NDA would not violate the [Posse Comitatus Act], given the express statutory authorization and the military-purpose of a commander's traditional protective power," Deputy Assistant Attorney General William Hyde said in his opinion.

     The Trump administration has so far set up six national defense areas along the southern border, in Arizona, California, New Mexico and Texas. But Friday's opinion said the military has suggested it may designate additional zones in the future.

     Since the national defense areas encompass wide strips of land that might not appear to be part of a military base, the Defense Department in some areas has put up signs in both English and Spanish warning that the area is restricted and unauthorized entry is prohibited.