The Supreme Court yesterday declined to let President Donald Trump deploy federalized National Guard members in the Chicago area to protect immigration agents and facilities from protests that have sometimes turned violent. Although the decision is preliminary, it casts serious doubt on the broad authority that Trump has claimed under 10 USC 12406, which allows him to "call into Federal service members and units of the National Guard of any State" in specified circumstances.

As relevant here, the third subsection of that law permits federalization when the president is "unable with the regular forces to execute the laws of the United States." Trump has invoked that provision to justify National Guard deployments in California, Oregon, and Tennessee as well as Illinois. While litigation over those deployments has mainly involved the question of what it means to say the president is "unable" to enforce federal law, the Supreme Court's ruling in Trump v. Illinois focuses on a different issue: What are "the regular forces"?

U.S. District Judge April Perry addressed that question after Illinois challenged Trump's use of National Guard personnel from Illinois and Texas to assist his immigration crackdown in Chicago. When Perry issued a temporary restraining order (TRO) against that deployment on October 10, she cited "several historical sources" indicating that "the phrase 'regular forces' was understood at the time of enactment to mean the soldiers and officers regularly enlisted with the Army and Navy, as opposed to militiamen who did not make it their livelihoods to serve their country but instead took up arms only when called forth in times of national emergency."

Trump "made no attempt to rely on the regular forces before resorting to federalization of the National Guard," Perry noted. "Nor do Defendants argue (nor is there any evidence to suggest) that the President is incapable with the regular forces of executing the laws. Therefore, the statutory predicate contained within Section 12406(3) has not been met on that basis alone."

The Trump administration asked the U.S. Court of Appeals for the 7th Circuit to block Perry's TRO while the case was pending, and it declined to do so on October 16. Although the 7th Circuit's did not discuss the meaning of "the regular forces," the Supreme Court expressed interest in that issue after the Trump administration the justices for a stay. In supplemental briefs, U.S. Solicitor General D. John Sauer that "the regular forces" refers to civilian law enforcement officers, while Illinois Solicitor General Jane Notz the Court to accept Perry's reading.