CBP “in this relationship is the owner of the mission pertaining to border security,” said retired Major General Merdith W.B. Temple, who served as the acting chief of engineers and the acting commanding general of the Army Corps of Engineers from 2011 to 2012. But the corps provides the necessary technical know-how. Back in 2006, for example, after Bush authorized double-layer fencing along the border, CBP “did not have an organic or inherent engineering capability” to handle the project on its own, Temple explained, and thus needed assistance.
But using the military for more permanent security tasks would be unprecedented, Kohn argued. “The use of the U.S. military for something other than fighting world wars is a long American tradition,” he said. “But to [do so] at this moment in time, when you have a major beefing-up of Immigration and Customs Enforcement and [the] border-security agency, and all other institutions and organizations and agencies in DHS, to use the U.S. military just for common, everyday operations is not appropriate and would be contested.”
There are legal limits on what DOD can do at the border. A 2013 Congressional Research Service report spelled out the extent to which the department can provide DHS reinforcement: While the military has “general legislative authority that allows it to provide support to federal, state, and local law enforcement agencies (LEAs) in counterdrug and counterterrorism efforts, and in combating certain border-related immigration and smuggling crimes,” other actions would require congressional authorization.
That includes having DOD take the reins entirely on the funding, construction, and monitoring of the border wall, Swift said. If Trump were to go that route, the challenge he’d face would be twofold: He would not only need congressional approval to use military funds for the wall, but he’d also need a separate authorization for DOD to administer the funds along the border.
Both steps would be tricky to pull off, if not impossible. If Trump wanted to dip into DOD funds already appropriated in the 2018 spending package, he’d need Congress’s OK, a Pentagon official told the Post. To set aside funds in next year’s budget, he would have to submit a budget amendment that would require 60 votes in the Senate—a threshold the upper chamber consistently struggles to meet on big pieces of legislation. As the Post’s sources noted, military officials, Democrats, and Republican defense hawks would likely oppose taking resources away from existing DOD projects and shifting them to the wall.
Given these potential challenges, the president could try to avoid Congress altogether and unilaterally direct DOD to fund the wall. To do so, the administration would have to find legislative language that allows the president to transfer funds for other purposes, said Saikrishna Bangalore Prakash, a law professor at the University of Virginia. “They need to read some language somewhere as appropriating money that can be used for a border wall, and it could be a combination of language that’s ordinarily thought of to be an authorization, or it could be in the appropriations bill,” Prakash said.