The work is being done under President Trump’s executive order of Jan. 25, which declared the administration’s policy to “secure the southern border of the United States through the immediate construction of a physical wall …” The order went on to set a high standard of effectiveness: “the prevention of all unlawful entries into the United States” along the border. Finally, the order cited an existing law, the Secure Fence Act, which in 2006 called for the construction of “at least two layers of reinforced fencing” and “additional physical barriers” on up to 700 miles of the 1,954-mile border.

“The executive order calls on the authority in the Secure Fence Act for us to begin immediately,” said a senior administration official who recently provided an extensive update on the state of the wall project. In March, U.S. Customs and Border Protection sent out a request for proposals for companies to bid on the construction of prototypes — not little models to sit on someone’s desk, but full-scale sections of proposed wall designs that will be put in place on the border. So far, Border Protection has received more than 100 proposals.

“We are evaluating what started out as a solicitation to industry and request for proposals — 18 to 30 feet high, concrete, impenetrable, hard-to-scale, the correct aesthetics,” the official said. “We’ve tried to capture the intent [of the executive order] in the requests for proposals, and those proposals are being evaluated now.”