Can the Department of Defense Build the Border Wall?

"According to multiple reports, President Trump may be contemplating declaring a national emergency in order to fund the construction of a physical barrier along the southern border with Mexico. The funding for such construction has been the focal point of the partial government shutdown that began on December 22, as Congress has thus far refused the President’s demand for $5.7 billion in funding for the construction of physical barriers by the Department of Homeland Security (DHS) (the lead agency responsible for deterring illegal border crossings). A number of media outlets have reported that the President is considering whether to resolve this impasse by directing the Department of Defense (DOD) to construct border fencing with its existing appropriations. Certain federal statutes potentially provide the DOD with limited authority to construct physical barriers along the border. However, the President may seek to avail himself of broader authorities by declaring a “national emergency” under the National Emergencies Act (NEA). Such a declaration could enable the President to invoke certain emergency military construction authorities established by the Military Construction Codification Act (MCCA). Whether these authorities—individually or in combination—extend to the construction of a border wall would present a reviewing court with several questions of first impression.

This Sidebar provides an overview of the NEA; the military construction authorities available in the event of a declared emergency that the Administration may rely upon to deploy border fencing; and other  statutory authorities that may provide the DOD with the authority to engage in certain construction operations..."
Border wall