In February 2019, after Congress approved some but not all the funding the Trump administration wanted for a wall on the Mexican border, the president declared a national emergency.

The next day, he issued a memorandum directing the Defense Department to support the Department of Homeland Security “in securing the southern border and taking other necessary actions to stop the flow of deadly drugs.” DHS then submitted a request for DoD’s assistance under a federal law (10 U.S.C. § 284) that allows the Pentagon to assist other agencies with the construction of fences, roads and lighting to block drug-smuggling corridors. The acting secretary of defense ultimately approved $2.5 billion for six projects across Arizona, California, and New Mexico.

This was an obvious end run around a Congress that specifically prohibited DoD from using its funding in that manner. In Section 8005 of the Department of Defense Appropriations Act of 2019, Congress authorized the secretary of defense to transfer certain funds between appropriations accounts upon “determination… that such action is necessary in the national interest.” But Section 8005 contains a proviso stating that such transfer authority may not be used in any case “where the item for which funds are requested has been denied by the Congress.”

The Sierra Club, a coalition of border-area community organizations, and the states of California and New Mexico sued, alleging that the border-wall reallocation violated statutory authority and thus also the Constitution’s Appropriations Clause, Article I, Section 9, which says that “no money shall be drawn from the Treasury, but in consequence of appropriations made by law.” A district court and then the U.S. Court of Appeals for the Ninth Circuit found that the acting secretary had indeed exceeded the scope of his powers.

Now before the Supreme Court, and building on our previous participation in the case, Cato filed a brief in support of the challengers. We urge the Court to reject the government’s self-serving argument that the acting secretary’s funding allocation can’t even be reviewed, which would close the judiciary’s doors to a broad class of lawsuits against executive lawmaking.

The Supreme Court will hear what at that point will be called Biden v. Sierra Club on February 22 — if the new administration doesn’t confess error and moot the case.