A discussion on a sister Stack Exchange site led me to ask this question.

Under what conditions can a branch of the military (excluding the Coast Guard for technical reasons) be used in an active role in law enforcement operations domestically in the United States? By active, I am envisioning active duty soldiers from the Army, Air Force, Navy or Marines breaking down doors and arresting suspects, so above and beyond manning checkpoints and road blocks or logistical operations in support of local law enforcement.

Can the President make this decision unilaterally acting under the Insurrection Act, or does he or she need the consent of Congress as specified in 18 U.S. Code § 1385?

If it depends, what does it depend on?

3 Answers 3


The use of the active duty military in a law enforcement role is not unconstitutional but it is prohibited by the posse comitatus act. 18 U.S.C. § 1385 (adopted 1878).

The text of the relevant legislation is as follows:

18 U.S.C. § 1385. Use of Army and Air Force as posse comitatus Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army or the Air 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.

Also notable is the following provision within Title 10 of the United States Code (which concerns generally the organization and regulation of the armed forces and Department of Defense):

10 U.S.C. § 375. Restriction on direct participation by military personnel The Secretary of Defense shall prescribe such regulations as may be necessary to ensure that any activity (including the provision of any equipment or facility or the assignment or detail of any personnel) under this chapter does not include or permit direct participation by a member of the Army, Navy, Air Force, or Marine Corps in a search, seizure, arrest, or other similar activity unless participation in such activity by such member is otherwise authorized by law.

The act does not apply to the National Guard mobilized at the request of a state governor. In practice, 10 U.S.C. § 375 has more bite because a federal prosecutor can and usually would refrain from prosecuting a crime ordered by his ultimate boss, the President, and there is not legal duty to prosecute every possible crime, but 10 U.S.C. § 375 creates an affirmative duty on the party of the Secretary of Defense that might be enforceable in a civil action.

  • 1
    The Posse Comitatus Act has exceptions, and 375 does not apply to many of those exceptions (it only applies to 10 USC Chapter 18, not Chapter 15 or any other exceptions present in federal law).
    – cpast
    Commented Oct 26, 2016 at 6:28
  • 1
    @ohwilleke This is good information, thank you. I understand much of the legality of any action taken by the Executive in reality would be decided after the fact, what I would like to know is whether there are boundary conditions in either case law or other statutes that one can look for during an action in order to make a best guess determination as to whether that ongoing action is in accordance with law or not. Commented Oct 26, 2016 at 14:09
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    The one exception would be Military Police (MP) units, which function as police officers on US Military bases and can make arrests of both military and civilian personnel within the base's Jurisdiction. They are military personnel acting in the capacity of police officers. Again, needs to be stressed that you must be on Base to be arrested by them.
    – hszmv
    Commented Mar 20, 2019 at 15:02
  • 1
    @hszmv MP jurisdiction is actually quite complicated (with more exceptions than this, and a rule that doesn't quite apply in all of the circumstances your comment implies), but the basic concept you are getting at had merit.
    – ohwilleke
    Commented Mar 20, 2019 at 19:01

You're misreading the Posse Comitatus Act. The law does not say "the military may not be used for law enforcement." It says "the military may not be used for law enforcement, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress." The Posse Comitatus Act was never about banning military use in law enforcement. It was designed to control military use in law enforcement. The title and text should be a hint about the actual effect of the law: there's a reason they talk about "posse comitatus."

Posse comitatus isn't the same as "law enforcement." It's a specific power law enforcement officers have, allowing them to command the assistance of able-bodied citizens to enforce the law (think "forming a posse," because that's what it is). Sheriffs traditionally had posse comitatus authority; so do federal marshals. At least for marshals, this authority was often used to get assistance from local soldiers. Soldiers were routinely used to back up the marshals. This could be done to enforce any federal law, and the marshals didn't have to try civilian methods first. This is what the text of the Posse Comitatus Act bans: routine use of the military by local authorities to enforce federal law. It was not intended to say "Congress must approve each specific use of the military." It does not in fact say that. It says "Congress and the Constitution can set out rules for the use of the military in law enforcement, but unless a law says the military can be used it can't be used." Source (CRS).

The provision letting marshals summon assistance doesn't explicitly say "including military assistance," so marshals can't summon military assistance. On the other hand, 42 USC § 1989 (warrants for certain civil rights crimes) does explicitly allow people executing the warrants to "summon and call to their aid [...] such portion of the land or naval forces of the United States, or of the militia, as may be necessary to the performance of the duty with which they are charged." So those warrants can be enforced by the military. 16 USC § 593 says the President may use the military to prevent illegal logging of federally owned timber in Florida.

And of course, you have the general law, predating the Posse Comitatus Act, which the Act was in no way meant to modify: the Insurrection Act. Remember how I said the Posse Comitatus Act was meant to deal with informal use of soldiers as a posse? The Insurrection Act represents what was considered an acceptable use of soldiers: authorized by the President himself, as the ultimate tool through which the United States exercises its sovereign authority within its borders. Source (CRS). Use of soldiers is a last resort; the President may only approve it under the Insurrection Act when he determines that the civil authorities are unwilling or unable to enforce the laws. The President must make a proclamation ordering those involved to disperse. But once the President has invoked the Insurrection Act, the Posse Comitatus Act does not apply. Under applicable DoD policy, enclosure 3, section 1.b, action under the Insurrection Act is a category of permissible direct assistance that is not restricted by law or DoD policy. A commander may choose not to deploy soldiers for law enforcement tasks (as happened in the LA riots), but the Insurrection Act perfectly falls under the exception in the Posse Comitatus Act (which is not surprising, seeing as it was written after the Insurrection Act with no intention of changing that law).

Interestingly enough, despite the Posse Comitatus Act apparently forbidding this, DoD policy recognizes two situations where the military may directly assist civil law enforcement in an emergency without any statutory authority. DoD bases this on implicit constitutional authority, specifically:

the inherent legal right of the U.S. Government - a sovereign national entity under the Federal Constitution - to insure the preservation of public order and the carrying out of governmental operations within its territorial limits, by force if necessary.

When there is an unexpected large-scale civil disturbance that local authorities are powerless to stop, local military commanders may intervene to stop widespread loss of life or wanton destruction and restore order to the point that civil authorities can take over, as well to protect federal property and functions if civil authorities cannot.

  • Would anyone care to explian the downvote?
    – cpast
    Commented Nov 1, 2016 at 3:29
  • 7
    I didn't down vote, but the Posse Comitatus Act is simply its common name. The act itself does more than forbidding law enforcement from the summoning of military personnel to be part of a posse and has an intended much broader scope. Your post provides an inaccurate impression of the scope of the law despite sounding plausible.
    – ohwilleke
    Commented Nov 30, 2016 at 17:45

I am in my car typing this so I don’t have the ability to backstop my answer. However, I recall an instance where the Obama administration was charged with and upheld with violating the Posse Comitatus Act.

The incident in question involved a robbery/ murder in a town near an Army base. Local law enforcement requested MP assistant in securing roads adjacent to the base and they the MPs approved the request. All hell broke lose. Because State authority was not consulted, that meant the Governor did not formally request National Guard Assistance. It was worse than that. Regular Army MPs performed therequested service under the direction of the local sheriff. When the story broke, the DoJ got involved and ruled violation of the Possie Comitus Act.

  • 2
    Can you backstop now? Because this sounds like Infowars nonsense.
    – bdb484
    Commented Nov 30, 2018 at 2:35

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