Defense Department and 10 U.S.C. 284: Legislative Origins and Funding Questions [February 20, 2019] [open pdf - 535KB]
From the Document: "On February 15, President Donald J. Trump confirmed recent reports that described the Administration's consideration of Department of Defense (DOD) authorities and funds to emplace physical barriers along the U.S.-Mexico border. A White House fact sheet detailed the potential availability of up to $8.1 billion 'to build the border wall'--including, among other authorities and funding sources, 'up to $2.5 billion under the Department of Defense funds transferred for Support for Counterdrug Activities (Title 10 United States Code, section 284).' The full title of the referenced authority is 'Support for Counterdrug Activities and Activities to Counter Transnational Organized Crime.' It is one of several DOD authorities to conduct counterdrug missions. In the context of Administration priorities along the southern border, this authority has gained congressional attention because its use is not contingent on the declaration of a national emergency."
CRS Insight, IN11052
Congressional Research Service: https://crsreports.congress.gov/