This from Congress’ Nonpartisan Research Arm, the Congressional Research Service
Can the Department of Defense build the Border Wall
“Drug corridors” are not defined in law, according to a top congressional aideAnother statute that authorizes the Secretary of Defense to assist civilian law enforcement with counterdrug activities may provide some authority for the construction of barriers along the border. 10 U.S.C. § 284 (Section 284) provides that the Secretary of Defense “may provide support for the counterdrug activities or activities to counter transnational organized crime” of any law enforcement agency, including through the “[c]onstruction of roads and fences and installation of lighting to block drug smuggling corridors across international boundaries of the United States.” …
Use of Section 284 would not require a declaration of a national emergency under the NEA. However, the DOD’s Section 284 authority to construct fences appears to extend only to “drug smuggling corridors,” a condition that may limit where DOD could deploy fencing.