[This post is co-authored with Professor Seth Barrett Tillman.]

The Supreme Court's decision in Trump v. Illinois (2025) was issued in a preliminary context, and without the benefit of oral argument. Some scholars have argued that this case is basically moot, but others believe the Executive Branch will continue litigating this case in the normal course. It would be problematic for the presidency to have this interim ruling remain on the books for generations to come, without a fulsome resolution by the Supreme Court.

We turn to the central statute at issue in the case.

10 U.S.C. § 12406(3) provides:

Whenever--the President is unable with the regular forces to execute the laws of the United States; …

(3) the President may call into Federal service members and units of the National Guard of any State in such numbers as he considers necessary to repel the invasion, suppress the rebellion, or execute those laws. Orders for these purposes shall be issued through the governors of the States or, in the case of the District of Columbia, through the commanding general of the National Guard of the District of Columbia. 

In Trump v. Illinois, the Court's focus was on the meaning of "regular forces," but there was less focus on the meaning of "unable." Here is the Court's analysis:

This interpretation means that to call the Guard into active federal service under §12406(3), the President must be "unable" with the regular military "to execute the laws of the United States." Because the statute requires an assessment of the military's ability to execute the laws, it likely applies only where the military could legally execute the laws. Such circumstances are exceptional: Under the Posse Comitatus Act, the military is prohibited from "execut[ing] the laws" "except in cases and under circumstances expressly authorized by the Constitution or Act of Congress." 18 U. S. C. §1385. So before the President can federalize the Guard under §12406(3), he likely must have statutory or constitutional authority to execute the laws with the regular military and must be "unable" with those forces to perform that function. [Slip. op. at *2.] 

Under the Court's view, the President is able to federalize the national guard only (i) when he has legal authority to deploy the regular forces domestically to execute the laws, and (ii) when those regular forces are insufficient. According to the Court's position, legal authority to use regular forces domestically to execute the laws is a necessary, but not a sufficient condition to federalize the National Guard. On the facts before it, the Court found that the Posse Comitatus Act prohibits the President from using the regular forces to execute the laws. [Slip op. at *2.] The Court concluded that President Trump could not federalize the National Guard because the President was "unable" to lawfully deploy the regular forces of the United States. In other words, the Court ruled against the President because he could not satisfy the necessary condition. But for the Court's argument to work, the President must be subject to the Posse Comitatus Act.

In Youngstown Sheet & Tube Co. v. Sawyer (1952), Justice Jackson took the position, absent analysis, that the President was bound by the Posse Comitatus Act. Jackson, a former Attorney General, wrote "Congress has forbidden [the President] to use the army for the purpose of executing general laws except when expressly authorized by the Constitution or by Act of Congress." This question was not at issue in Youngstown. To be sure, Jackson wrote his concurrence closer in time to when the Posse Comitatus Act was adopted. But it is not clear that Jackson's analysis still stands in light of the Court's more recent precedents. 

Let's walk through the analysis. The Posse Comitatus Act, 18 U.S.C. § 1385, provides:

Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army, the Navy, the Marine Corps, the Air Force, or the Space Force as a posse comitatus or otherwise to execute the laws shall be fined under this title or imprisoned not more than two years, or both. (emphasis added).

The Supreme Court's analysis in Trump v. Illinois turned on the President's inability to use the regular forces for purposes of domestic law enforcement. And this analysis relied on the President being subject to the Posse Comitatus Act. But does the Posse Comitatus Act apply to the President? To be sure, this argument has nothing to do with whether the President is an "officer of the United States." Rather, we rely on well developed principles of statutory interpretation. 

The statute does not expressly reference the President. Franklin v. Massachusetts (1992) and related cases articulated a clear statement rule. See also, e.g., Nixon v. Fitzgerald, 457 U.S. 731, 748 & n.27 (1982) (Powell, J.). Under this canon of avoidance, if the President is not expressly named in a statute, the courts should not presume that Congress intended to limit the President's power. The Office of Legal Counsel has recognized this clear statement rule. See also, e.g., Memorandum from William H. Rehnquist, Assistant Attorney General, for the Honorable Egil Krogh, Staff Assistant to the Counsel to the President, Office of Legal Counsel, Re: Closing of Government Offices in Memory of Former President Eisenhower 3 (Apr. 1, 1969); Memorandum from Antonin Scalia, Asst. Att'y Gen, to Honorable Kenneth A. Lazarus, Re: Applicability of 3 C.F.R. Part 100 to the Pres. and V.P., OLC, at 2 (Dec. 19, 1974). This sort of avoidance would be especially appropriate with the Posse Comitatus Act given that the statute potentially intrudes on the President's Article II powers.

Moreover, the Posse Comitatus Act imposes criminal penalties of up to two years in prison. Under the immunity doctrine from Trump v. United States (2024), a criminal prosecution against the President is likely barred where the statute implicates the President's "core" presidential powers. The Court concluded that "At least with respect to the President's exercise of his core constitutional powers, this immunity must be absolute." See Illinois v. Trump, Civil A. No. 25-cv-12174, 2025 WL 2886645, at *19 (N.D. Ill. Oct. 10, 2025) (April M. Perry, J.) ("The Posse Comitatus Act makes it a criminal offence to use the Army, Navy, Marine Corps, and Air Force to 'execute the laws' unless expressly authorized by Congress. 18 U.S.C. § 1385. And as Justice Jackson in his well-known Youngstown concurrence has recognized, while this prohibition likely does not apply to hold the President criminally liable, the Act nonetheless operates to 'forbid[ ]' the President 'to use the army for the purpose of executing general laws except when expressly authorized by the Constitution or by Act of Congress.' Youngstown Sheet & Tube Co., 343 U.S. at 644–45 (Jackson, J., concurring in the judgment)." (second set of italics added)), aff'd in part, rev'd in part, 155 F.4th 929 (7th Cir. 2025) (per curiam), stay denied, Trump v. Illinois, No. 25A443, 2025 WL 3715211, 607 U.S. —- (Dec. 23, 2025) (per curiam). 

In Trump v. United States, the majority opinion did not expressly reference the clear statement rule. Nevertheless, we believe the clear statement rule animated the Court's immunity analysis. The relevant criminal statutes that Trump had been charged with violating were generally worded, and did not expressly apply to the President. For example, during oral argument, Justice Kavanaugh asked John Sauer, counsel for defendant Trump, "I assume you would think that a clear statement has to be required, a clear statement in the statute covering the president, if the president's official acts are going to be criminalized?" Later, Kavanaugh told Sauer, "there's a lot of official powers that are not exclusive to the president under his Article II authority, but for those, I understood you to be saying, at a minimum, there would need to be a clear statement in the statute referencing the president so that the president's on notice and can conduct himself or herself accordingly." Sauer replied, "That's absolutely correct, and that would be consistent both with Franklin [v. Massachusetts] and and Public Citizen [v. Department of Justice] and [other] cases--a long series of other clear statement rule cases."

We think Justice Barrett read the majority opinion the same way we do here. Indeed, Justice Barrett, in her partial concurrence, felt the need to reject the application of this substantive canon because she understood the majority to be following this canon. She said she would not apply either the "avoidance canon" or the "clear-statement rule." Justice Barrett favorably cited Justice Kennedy's Public Citizen concurrence which declined to apply the avoidance canon.

The Posse Comitatus Act does not expressly reference the President by name, and it also arguably intrudes on "core" presidential powers. For these reasons, the clear statement rule and the immunity doctrine work in tandem and are mutually supporting. Working together, these doctrines reinforce that the President would not be subject to the Posse Comitatus Act. In Trump v. Illinois, the Supreme Court did not have occasion to address the applicability of Trump v. United States' presidential immunity doctrine with regard to the Posse Comitatus Act.

The Trump v. United States immunity doctrine would only shield the President against a prosecution, but that doctrine would not shield his subordinates involved in law execution subject to the President's direction. By contrast, a rogue military commander who unilaterally directs military subordinates to engage in law execution would face liability under the Posse Comitatus Act. But we do not think it is so clear that a commander violates the statute if the commander follows the President's otherwise lawful order, after the President has given orders to direct the regular forces to engage in law execution. In this set of circumstances, we suggest that it is the President, and not the commander, who has "willfully" directed regular forces to engage in law execution. "An act is done 'willfully' if done voluntarily and intentionally and with the specific intent to do something the law forbids." (emphases added) U.S. Department of Justice, U.S Attorneys' Manual/Criminal Resource Manual, Section 910 Knowingly and Willfully. It is not frivolous to suggest that an act taken by a subordinate military officer carrying out a superior's orders (including the President's) is not a "voluntary" act, and therefore, such an act is not "willful." Likewise, depending on the circumstances, such a subordinate military officer may also lack "the specific intent to do something the [Posse Comitatus Act] forbids." But, in any event, we do not need to settle this subsidiary legal issue here.

Relatedly, are Article III judges subject to the Posse Comitatus Act? If an Article III judge has a case before him, where the court has subject matter jurisdiction, and the judge issues an order, but it is not enforced by the U.S. Marshals, such a judge might**—rightly or wrongly—**call out a posse composed of the regular forces to enforce his judicial orders. Cf. Ex parte Merryman 17 F. Cas. 144 (1861) (No. 9487) (Taney, C.J., in chambers) ("[T]he chief justice said, that the marshal had the power to summon the posse comitatus to aid him in seizing and bringing before the court, the party named in the attachment, who would, when so brought in, be liable to punishment by fine and imprisonment; but where, as in this case, the power refusing obedience was so notoriously superior to any the marshal could command, he [the chief justice] held that officer excused from doing anything more than he had done."). This hypothetical is perhaps not so far-fetched. In recent months, federal judges have worried that the Trump Administration would withdraw U.S. Marshals Service's protection from federal judges. Any effort to criminally prosecute an Article III judge for his error (assuming this course of action to be an error) would be blocked by the doctrine of absolute judicial immunity. 

We recapitulate our position. First, there is a substantial argument that the Posse Comitatus Act does not apply to the President in light of the clear statement rule. Second, even assuming the President is subject to the Posse Comitatus Act, the doctrine announced in Trump v. United States, insofar as the Posse Comitatus Act intrudes on "core" executive powers, immunizes the President against prosecution. Third, subordinate military officers, in compliance with Presidential orders, who direct their subordinates to engage in law-execution, are not voluntarily and willfully violating the Posse Comitatus Act. If any of these arguments are correct, then we think the emergency docket ruling in Trump v. Illinois, that the President is unable to use the regular forces and the federalized National Guard, warrants some further scrutiny when this case returns to the merits docket.