Trump just delegated authority to Wilbur Ross, Sec Of Commerce, to use the military to build the wall, lol, using the John Mcain defense act..
Military Construction Authorization Act for Fiscal Year 2019
The bill authorizes appropriations and sets forth policies regarding military construction for the Army, Navy, Air Force, defense agencies, the North Atlantic Treaty Organization Security Investment Program, and Guard and Reserve Forces facilities.
https://www.congress.gov/bill/115th-congress/house-bill/5515
https://www.whitehouse.gov/presidential-actions/presidential-memorandum-secretary-commerce-2/