Amicus Curiae Brief — Donald J. Trump, President of the United States, et al., Applicants v. Illinois, et al.

No. 25A443

In the Supreme Court of the United States

DONALD J. TRUMP, et al.,

Applicants,

v.

STATE OF ILLINOIS, et al.,

Respondents.

BRIEF OF THE STATES OF CALIFORNIA AND OREGON AS

AMICI CURIAE IN SUPPORT OF RESPONDENTS

DAN RAYFIELD

Attorney General of Oregon

BENJAMIN GUTMAN

Solicitor General

ROB BONTA

Attorney General of California

SAMUEL T. HARBOURT

Solicitor General

HELEN H. HONG

Principal Deputy

Solicitor General

CHRISTOPHER D. HU

AARON D. PENNEKAMP*

Deputy Solicitors General

HALEY L. AMSTER

Associate Deputy

Solicitor General

STATE OF CALIFORNIA

DEPARTMENT OF JUSTICE

1300 I Street, Suite 125

P.O. Box 944255

Sacramento, CA 94244-2550

(916) 210-6661

Aaron.Pennekamp@doj.ca.gov

*Counsel of Record

November 10, 2025

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TABLE OF CONTENTS

Page

Interest of amici curiae and summary of argument .......................................... 1

Argument ............................................................................................................. 3

Conclusion.......................................................................................................... 12

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INTEREST OF AMICI CURIAE AND SUMMARY OF ARGUMENT

California and Oregon have challenged the federal government’s reliance

on Section 12406 to deploy members of the National Guard to the streets of

their cities. See, e.g., Oregon v. Trump, __ F.4th __, 2025 WL 3013134 (9th Cir.

Oct. 28, 2025) (en banc); Newsom v. Trump, 141 F.4th 1032 (9th Cir. 2025).

Those ongoing cases implicate many of the same legal questions addressed in

the briefing before the Court here. In light of amici’s profound interest in the

proper resolution of those questions, they previously filed or joined amicus

briefs in support of respondents in this proceeding.

As amici have explained, see, e.g., Br. of State & Governor of California

20-24 (Br. of California), and as the Seventh Circuit provisionally recognized,

see App’x 98a-100a, Section 12406 does not support the federal government’s

extraordinary attempt to deploy members of the military in Chicago. Congress

enacted Section 12406 to address invasions, rebellions, and other “unusual and

extreme exigencies.” Newsom, 141 F.4th at 1051; see also Br. of Maryland,

Washington, Oregon et al. 8-9. Nothing of the kind has occurred in Chicago—

or anywhere else in the United States—over the past year.

The federal

government’s attempt to call forth and deploy the military notwithstanding the

absence of any such exigency threatens profound harm to our Nation’s

democratic traditions, as well as the balance of power among the States,

Congress, and the Executive Branch. The Framers carefully designed our

constitutional system to leave principal control over the militia—today, the

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National Guard—at the state level, subject to federalization on narrow

grounds authorized by Congress. See, e.g., Br. of California 5-6.

In addressing the federal government’s request for a stay, the Seventh

Circuit identified two plausible interpretations of “the regular forces” in

Section 12406(3): federal civilian officers and “the soldiers and officers serving

in the regular armed forces.”

App’x 100a.

In their prior briefing, amici

generally focused on the first of these interpretations.

See, e.g., Br. of

California 21. California and Oregon submit this brief to supplement that

prior briefing and address the latter.

As a textual and historical matter, it is certainly reasonable to construe

“regular forces” to refer to members of the regular military. Indeed, some

experts in this area of law have raised powerful arguments that the term “can’t

possibly be” understood any other way. 1 To date, the federal government’s

principal response has been that the term “regular forces” “naturally refers to”

civilian personnel because military forces “do not regularly ‘execute the law.’”

Appl. 30 n.4. That response is unpersuasive: the military can sometimes play

a role in “executing the laws” during the types of unusual and extreme

exigencies that Congress designed Section 12406 to address. Because no such

exigencies exist in present-day Chicago, however, neither members of the

1 E.g., Vladeck, The State of Play in the National Guard Cases, One First (Oct.

23, 2025), https://tinyurl.com/2erx5p5n.

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National Guard nor any other military forces have a proper role to play in

executing the laws there at this time.

ARGUMENT

1. Statutory interpretation begins “with the text of the statute.”

Bartenwerfer v. Buckley, 598 U.S. 69, 74 (2023) (internal quotation marks

omitted). As Professor Martin Lederman has explained, “the use of the term

‘the regular forces’ . . . to refer to military personnel . . . [was] commonplace in

federal law and, more broadly, in writings within all three branches” in the

early twentieth century when the relevant statutory text was enacted. Br. of

Prof. Lederman 13; see id. at 8-19. For example, in McClaughry v. Deming,

186 U.S. 49, 56 (1902), this Court used the term “regular forces” to distinguish

between “the Regular Army” or “regulars,” on the one hand, and “the men

composing the militia,” on the other. The provision that comes directly before

Section 12406 in Title 10 likewise uses the term “regular” in this way, referring

to “members of the Regular Army or Regular Air Force.” 10 U.S.C. § 12405.

“[A] legislative body generally uses a particular word with a consistent

meaning in a given context.” Erlenbaugh v. United States, 409 U.S. 239, 243

(1972). And today, Title 10—where Section 12406 is codified—defines the term

“regular” to mean “enlistment, appointment, grade, or office in a regular

component of an armed forces.” 10 U.S.C. § 101(b)(12); see generally Digital

Realty Tr., Inc. v. Somers, 583 U.S. 149, 160 (2018) (“‘When a statute includes

an explicit definition, we must follow that definition[.]’”).

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The history and context of Section 12406 provide further support for

defining “regular forces” to mean the regular military. When Congress enacted

the first version of Section 12406 in 1903, it referred to “the other forces at [the

President’s] command,” rather than “regular forces.”

32 Stat. 775, 776.

“Forces” and “command” are generally military terms.

See, e.g., Dep’t of

Defense, Dictionary of Military and Associated Terms 34, 68 (2025).

In

common parlance, “forces at [the President’s] command” would not be the most

natural way to refer to civilian personnel. And there is no indication that

Congress intended to refer to nonmilitary forces when it replaced “forces at his

command” with “regular forces” in 1908. See 35 Stat. 399, 400. To the contrary,

the Secretary of War explained that the amendments were designed to ensure

that “the organized militia [could] be called into . . . service” when “the military

needs of the Federal Government . . . can not be met by the regular forces.”

App’x 55a (quoting H.R. Rep. No. 60-1067, at 6 (1908)).

Although the Ninth Circuit appeared to assume “regular forces” means

civilian personnel, see Newsom, 141 F.4th at 1052, it did not reach any

definitive conclusion to that effect. The court addressed justiciability at some

length, see id. at 1045-1046, as well as the standard for applying the statute to

the facts at hand, see id. at 1046-1051, but it said relatively little about how to

construe the plain terms of Section 12406(3). That approach may have been

influenced by the highly expedited timeline for issuing a decision, see id. at

1042-1043, as well as the shifting nature of the federal government’s position

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on Section 12406.

The federal government originally defended its

federalization under Section 12406(2) alone, see Newsom v. Trump, No. 253727 (9th Cir.), C.A. Dkt. 57.1 at ER-190; then invoked Section 12406(3) and

took the view that “regular forces” refers to “everything other than the State

National Guard,” including “the Marines” and “local police,” Newsom v. Trump,

No. 25-cv-4870 (N.D. Cal.), D.Ct. Dkt. 63 at 24; and then switched gears and

argued that the “regular forces” refers only to civilian agents, see Newsom v.

Trump, No. 25-3727 (9th Cir.), C.A. Dkt. 23.1 at 5.

As the case proceeds beyond the preliminary stage, the Ninth Circuit may

revisit its tentative understanding of “regular forces.” Indeed, one member of

the panel considering the merits of the case recently observed that the court’s

stay-stage opinion was “somewhat ambiguous” about the requirements of

Section 12406(3). Argument at 14:27-28, Newsom v. Trump, No. 25-3727 (9th

Cir. Oct. 22, 2025) (Miller, J.), https://tinyurl.com/a99x3bjf. The same member

of the court also questioned the federal government about an interpretation of

Section 12406(3) quite similar to the one addressed in this Court’s recent

supplemental-briefing order. Id. at 18:26-18:44; see Br. of Historian Mark

Graber, Newsom v. Trump, No. 25-3727 (9th Cir.), C.A. Dkt. 76.1 at 26 (arguing

6

that Section 12406(3) applies only in extreme exigent circumstances, not when

“civil law is operative and courts are functioning”). 2

2. The federal government’s principal response has been that the term

“regular forces” “naturally refers to” civilian personnel because military forces

“do not regularly ‘execute the law.’” Appl. 30 n.4. As the federal government

points out, see id., the Posse Comitatus Act generally forbids members of the

military from engaging in civilian law-enforcement activities, see generally

United States v. Dreyer, 804 F.3d 1266, 1275 (9th Cir. 2015) (en banc). The

Act’s prohibition is not categorical, however. It leaves two narrow paths for

the military to lawfully execute the laws in certain circumstances.

The first is where a statutory exception applies. The Posse Comitatus Act

allows the military to engage in otherwise prohibited forms of law enforcement

when “expressly authorized [to do so] by . . . Act of Congress.” 18 U.S.C. § 1385.

One of more than two dozen statutory exceptions is “the Insurrection Act,” the

collective name for several provisions that appear at 10 U.S.C. §§ 251-255. See

App’x 75a (collecting examples).

The requirements for invoking the

2 In the Newsom litigation, California has generally proceeded to date on the

assumption that “regular forces” refers to civilian personnel. See, e.g., Newsom

v. Trump, No. 25-3727 (9th Cir.), C.A. Dkt. 63.1 at 22-28. But the State has

also explained that it would be reasonable as a textual and historical matter

to construe “regular forces” to mean members of the regular military. See

Newsom v. Trump, No. 25-3727 (9th Cir.), C.A. Dkt. 130.1 at 1-2. California

and Oregon recently took the same position in a joint filing in ongoing

proceedings before the U.S. District Court for the District of Oregon. See

Oregon v. Trump, No. 25-cv-1756 (D. Or.), D.Ct. Dkt. 130 at 5-8.

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Insurrection Act are demanding. See, e.g., Use of Marshals, Troops, and Other

Federal Personnel for Law Enforcement in Mississippi, 1 Supp. Op. O.L.C. 493,

496 (1964). Presidents throughout our history have invoked it only when

necessary to confront “situations where state and local law enforcement have

completely broken down.” Id.; see, e.g., Br. of Former U.S. Army & Navy

Secretaries & Retired Four-Star Admirals & Generals 22-23; cf. Vladeck, The

Field Theory: Martial Law, the Suspension Power, and the Insurrection Act, 80

Temp. L. Rev. 391, 432-434 (2007) (examining whether the Insurrection Act

authorizes “martial law,” i.e., the temporary and extraordinary imposition of

military control during a crisis in which civilian authorities fail). 3

The second way for the military to lawfully execute the laws is to

undertake activities that do not fall within the Posse Comitatus Act’s

prohibitions in the first place. By its terms, the statute bars the “use[] [of] any

part of the [Armed Forces] as a posse comitatus or otherwise to execute the

3 As a matter of first principles, it is debatable whether the Insurrection Act

“expressly authorize[s]” the activities prohibited by the Posse Comitatus Act.

18 U.S.C. § 1385 (emphasis added). But soon after the Act was passed, the

federal government took the position that the Insurrection Act operates as an

exception. See, e.g., Dep’t of War Gen. Order 49 (July 7, 1878), reproduced at

https://tinyurl.com/4mwavjcs.

The federal government has consistently

adhered to that view, see, e.g., Dep’t of Def. Directive 5525.5, Encl. 4 (Jan. 15,

1986), https://tinyurl.com/mr4dzhvk, and Congress has never abrogated it in

the many amendments of the Posse Comitatus Act and Insurrection Act. It is

thus reasonable to presume that Congress was “aware of [this] . . .

interpretation” and intended “to adopt [it].” Lorillard v. Pons, 434 U.S. 575,

580 (1978). By contrast, until earlier this year, the federal government had

never taken the position that Section 12406(3) operates as an exception to the

Posse Comitatus Act. See Newsom v. Trump, __ F. Supp. 3d __, 2025 WL

2501619, at *15 (N.D. Cal. Sept. 2, 2025).

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laws.” 18 U.S.C. § 1385. While the phrase “otherwise . . . execute the laws”

may “seem[] sweeping” in isolation, Elsea, Cong. Rsch. Serv., R42659, The

Posse Comitatus Act & Related Matters 56 (2018), courts typically avoid

“untethering an ‘otherwise’ provision from the rest of a criminal statute,”

Fischer v. United States, 603 U.S. 480, 488 (2024). “Execute the laws” thus

refers to law-enforcement activities akin to those historically performed “as a

posse comitatus”: the forms of assistance historically provided to local sheriffs

to prevent civil disorder. See Dreyer, 804 F.3d at 1272. Consistent with that

view, Congress has long understood the Posse Comitatus Act to cover “search,

seizure, arrest, or other similar activity.” Dreyer, 804 F.3d at 1275 (quoting 10

U.S.C. § 375). 4 On that understanding, the military may lawfully engage in a

narrow range of domestic activities without implicating the Posse Comitatus

Act, such as mail delivery during a postal strike, see, e.g., Rubio, Undelivered:

From the Great Postal Strike of 1970 to the Manufactured Crisis of the U.S.

Postal Service 97-111 (2020), or distribution of food and medicine following a

natural disaster, see, e.g., McGrane, Katrina, Federalism, and Military Law

Enforcement, 108 Mich. L. Rev. 1309, 1317-1318 (2010).

also Dep’t of Def. Instr. 3025.21, Encl. 3 § 1.c(1) (Feb. 27, 2013),

https://tinyurl.com/46mszeur

(memorializing

Defense

Department’s

longstanding views about the types of law-enforcement activities barred by the

Posse Comitatus Act); cf. Kealy, Reexamining the Posse Comitatus Act, 21 Yale

L. & Pol’y Rev. 383, 404 (2003) (“[T]he closer the role of the military personnel

comes to that of a police officer on the beat, the greater the likelihood that the

Act is being violated.”) (internal quotation marks omitted).

4 See

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Contrary to the federal government’s suggestion, see Oregon v. Trump,

No. 25-cv-1756 (D. Or.), D.Ct. Dkt. 131 at 8, it would not have been “strange”

for Congress to contemplate the circumstances discussed above when crafting

Section 12406(3). Statutory terms are “known by the company [they] keep[].”

Gustafson v. Alloyd Co., 513 U.S. 561, 575 (1995).

Given that Sections

12406(1)-(2) address “unusual and extreme exigencies,” Newsom, 141 F.4th at

1051, it is logical to think Congress had in mind circumstances akin to

invasions and rebellions when drafting Section 12406(3). And as evidenced by

the examples discussed above, see supra pp. 7-8, the situations in which the

military can lawfully execute the laws tend to be large-scale disasters, crises,

and other emergencies.

The federal government has also suggested that construing “regular

forces” to mean regular military forces would be inconsistent with “a strong

historical norm” that favors reliance on the militia before calling on “the fulltime standing military.” Oregon v. Trump, No. 25-cv-1756 (D. Or.), D.Ct. Dkt.

131 at 5. In making that argument, the federal government principally relies

on preferences expressed “[a]t the founding”—not prevailing views in the early

twentieth century when Congress enacted Section 12406(3). Id. at 5-6 (citing,

e.g., Federalist No. 29 (Alexander Hamilton)). At the founding, there was a

“widespread fear [of] a national standing Army.” Perpich v. Dep’t of Def., 496

U.S. 334, 340 (1990). Our Nation’s early leaders hoped that a “Uniform Militia

throughout the United States” would be able to provide for an adequate

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national defense. Id. at 341. But that effort “failed to provide for a capable

military force,” Leider, Deciphering the “Armed Forces of the United States,” 57

Wake Forest L. Rev. 1195, 1225 (2022), and “the federal government

increasingly relied on the regular army,” id. at 1225—including in the rare

circumstances in which the military was deployed domestically, see id. at 12251226. By 1903, “the militia proved to be . . . decidedly unreliable[.]” Perpich,

496 U.S. at 340; see Leider, supra, at 1227-1228. In light of that history, it is

not at all surprising that Congress viewed the National Guard as a backup

option to the regular military, not a first-line response force.

Nor, finally, would it hamper federal law-enforcement operations to

construe “regular forces” to mean regular military forces. Cf. Appl. 36-40.

Section 12406 has been invoked—at most—only one time since its 1903

enactment. See, e.g., Br. of California 4 & n.2; Br. of Prof. Lederman 18 & n.11.

With that single exception, in the rare instances during the twentieth century

when the President has deployed the National Guard or regular military

domestically, he has relied on other statutory authorities—in particular, the

Insurrection Act. See, e.g., Br. of Former U.S. Army & Navy Secretaries &

Retired Four-Star Admirals & Generals 22-23. If there is a need for additional

authority to federalize the National Guard, Congress can provide it. Cf. Nat’l

Fed. Independent Bus. v. OSHA, 595 U.S. 109, 118 (2022) (refusing to

“significantly expand [an executive agency’s] authority without clear

congressional authorization”).

The Framers entrusted Congress, not the

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President, to determine when federalization is appropriate. See U.S. Const.

art. I, § 8, cls. 15-16.

* * *

The federal government’s attempt to invoke Section 12406(3) in this case

calls to mind concerns raised by skeptics and opponents of our new

constitutional charter during debates over ratification. Patrick Henry, for

example, warned that the President could call forth state militias “to enforce

every execution [of the laws] indiscriminately.” App’x 49a (quoting 3 Elliot,

The Debates in the Several State Conventions on the Adoption of the Federal

Constitution 412 (1836)). Madison and Hamilton responded forcefully to refute

those suggestions and reassure doubters that the President would be unable

to wield that far-reaching authority. See, e.g., id. at 48a-49a.

Since the Founding, Congress and the Judiciary have honored the

Framers’ vision, taking steps necessary to ensure that our Nation does not take

even one step down the road of unnecessary military intrusion into civilian

affairs. See, e.g., Youngstown Sheet & Tube Co. v. Sawyer, 343 U.S. 579, 586589 (1952); Duncan v. Kahanamoku, 327 U.S. 304, 315 (1946); Ex Parte

Milligan, 71 U.S. 2, 121 (1866). As Justice Murphy once reminded us, “[t]hose

who founded this nation” “shed their blood to win independence from a ruler

who they alleged was attempting to render the ‘military independent of and

superior to the civil power[.]’”

concurring).

Duncan, 327 U.S. at 325 (Murphy, J.,

Similarly, Justice Scalia explained that “[a] view of the

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Constitution that gives the Executive authority to use military force rather

than the force of law against citizens on American soil flies in the face of the

mistrust [of British rule] that engendered” our constitutional order. Hamdi v.

Rumsfeld, 542 U.S. 507, 569 (2004) (Scalia, J., dissenting). “[S]upremacy of

the civil over the military is one of our great heritages.” Duncan, 327 U.S. at

325 (Murphy, J., concurring).

This case poses a profound test of our

commitment to that longstanding principle, which has guided our democracy

for generations and has “made possible the attainment of a high degree of

liberty regulated by law rather than by caprice.” Id.

CONCLUSION

The application for a stay should be denied.

Respectfully submitted,

DAN RAYFIELD

Attorney General of Oregon

BENJAMIN GUTMAN

Solicitor General

November 10, 2025

ROB BONTA

Attorney General of California

SAMUEL T. HARBOURT

Solicitor General

HELEN H. HONG

Principal Deputy Solicitor General

CHRISTOPHER D. HU

AARON D. PENNEKAMP

Deputy Solicitors General

HALEY L. AMSTER

Associate Deputy Solicitor General