The CRS "legal sidebar" outlines alternative paths for the president, who has been considering tapping the National Emergencies Act.

The Congressional Research Service , Capitol Hill's think tank, is highlighting laws for Trump to tap that would not be subject to Congress' "termination provison."

Law professor John Banzhaf (often called a "gadfly" for his embrace of heterodox positions) elaborates:

[T]he authority for such a move has very recently been provided by the impartial and highly respected Congressional Research Service, notes public interest law professor John Banzhaf.

It said:

"A separate emergency military construction statute may also provide the President with certain limited authorities to construct barriers along the border without declaring a national emergency.

10 U.S.C. § 2803 (Section 2803) provides that the Secretary of Defense "may carry out a military construction project not otherwise authorized by law" upon determining that (1) "the project is vital to the national security or to the protection of health, safety, or the quality of the environment," and (2) "the requirement for the project is so urgent that" deferring the project "would be inconsistent with national security or the protection of health, safety, or environmental quality."

"10 U.S.C. § 284 (Section 284) provides that the Secretary of Defense "may provide support for the counterdrug activities or activities to counter transnational organized crime" of any law enforcement agency, including through the "[c]onstruction of roads and fences and installation of lighting to block drug smuggling corridors across international boundaries of the United States." Use of Section 284 Would not require a declaration of a national emergency under the NEA."

Both statutes have built-in limitations, and a invocation of either or both statutes to help fund a border wall would, of course, be challenged. ...

Although either rationale would be questioned by opponents, courts have traditionally been very deferential to determinations made by presidents regarding issues of national security and drug smuggling.

Indeed, courts may well question whether a rancher whose land is being taken under eminent domain for a wall would have legal standing to contest in court not only the amount of compensation he is entitled to, but also the legality of the entire project as ordered by any president himself.

Similarly, it may seem highly inappropriate for a single judge somewhere in the U.S., chosen by opponents of the wall because of his leanings and prior decisions, to second guess any president on "vital" matters of "national security," and to issue an injunction halting the entire project based upon his own views.