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The Posse Comitatus Act Explained

The law generally prevents the president from using the military as a domestic police force.

Published: October 14, 2021

The Posse Comit­atus Act bars federal troops from parti­cip­at­ing in civil­ian law enforce­ment except when expressly author­ized by law. This 143-year-old law embod­ies an Amer­ican tradi­tion that sees milit­ary inter­fer­ence in civil­ian affairs as a threat to both demo­cracy and personal liberty. However, recent events have revealed danger­ous gaps in the law’s cover­age that Congress must address.

What does the term “posse comit­atus” mean?

In Brit­ish and Amer­ican law, a posse comit­atus is a group of people who are mobil­ized by the sher­iff to suppress lawless­ness in the county. In any clas­sic West­ern film, when a lawman gath­ers a “posse” to pursue the outlaws, they are form­ing a posse comit­atus. The Posse Comit­atus Act is so named because one of the things it prohib­its is using soldiers rather than civil­ians as a posse comit­atus.

What are the origins of the Posse Comit­atus Act?

The Posse Comit­atus Act was passed in 1878, after the end of Recon­struc­tion and the return of white suprem­acists to polit­ical power in both south­ern states and Congress. Through the law, Congress sought to ensure that the federal milit­ary would not be used to inter­vene in the estab­lish­ment of Jim Crow in the former Confed­er­acy.

Despite the igno­mini­ous origins of the law itself, the broader prin­ciple that the milit­ary should not be allowed to inter­fere in the affairs of civil­ian govern­ment is a core Amer­ican value. It finds expres­sion in the Consti­tu­tion’s divi­sion of power over the milit­ary between Congress and the pres­id­ent, and in the guar­an­tees of the Third, Fourth, Fifth, and Sixth Amend­ments, which were in part reac­tions to abuses commit­ted by the Brit­ish army against Amer­ican colon­ists.

Today, the Posse Comit­atus Act oper­ates as an exten­sion of these consti­tu­tional safe­guards. Moreover, there are stat­utory excep­tions to the law that allow the pres­id­ent to use the milit­ary to suppress genu­ine rebel­lions and to enforce federal civil rights laws.

What does the Posse Comit­atus Act say?

The Posse Comit­atus Act consists of just one sentence: “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.”

In prac­tice, this means that members of the milit­ary who are subject to the law may not parti­cip­ate in civil­ian law enforce­ment unless doing so is expressly author­ized by a stat­ute or the Consti­tu­tion.

Are all members of the milit­ary covered by the Posse Comit­atus Act?

No, only federal milit­ary person­nel are covered. While the Posse Comit­atus Act refers only to the Army and Air Force, a differ­ent stat­ute extends the same rule to the Navy and Marine Corps. The Coast Guard, though part of the federal armed forces, has express stat­utory author­ity to perform law enforce­ment and is not bound by the Posse Comit­atus Act.

Members of the National Guard are rarely covered by the Posse Comit­atus Act because they usually report to their state or territ­ory’s governor. That means they are free to parti­cip­ate in law enforce­ment if doing so is consist­ent with state law. However, when Guard person­nel are called into federal service, or “feder­al­ized,” they become part of the federal armed forces, which means they are bound by the Posse Comit­atus Act until they are returned to state control.

What are the main stat­utory excep­tions to the Posse Comit­atus Act?

There are many stat­utory excep­tions to the Posse Comit­atus Act, but the most import­ant one is the Insur­rec­tion Act. Under this law, in response to a state govern­ment’s request, the pres­id­ent may deploy the milit­ary to suppress an insur­rec­tion in that state. In addi­tion, the Insur­rec­tion Act allows the pres­id­ent — with or without the state govern­ment’s consent — to use the milit­ary to enforce federal law or suppress a rebel­lion against federal author­ity in a state, or to protect a group of people’s civil rights when the state govern­ment is unable or unwill­ing to do so.

What are the consti­tu­tional excep­tions to the Posse Comit­atus Act?

There are no consti­tu­tional excep­tions to the Posse Comit­atus Act. The law allows only for express excep­tions, and no part of the Consti­tu­tion expressly empowers the pres­id­ent to use the milit­ary to execute the law. This conclu­sion is consist­ent with the law’s legis­lat­ive history, which suggests that its drafters chose to include the language about consti­tu­tional excep­tions as part of a face-saving comprom­ise, not because they believed any exis­ted.

This has not stopped the Depart­ment of Defense from claim­ing that consti­tu­tional excep­tions to the law exist. The Depart­ment has long claimed that the Consti­tu­tion impli­citly gives milit­ary command­ers “emer­gency author­ity” to unilat­er­ally use federal troops “to quell large-scale, unex­pec­ted civil disturb­ances” when doing so is “neces­sary” and prior author­iz­a­tion by the pres­id­ent is impossible. In the past, the depart­ment also claimed an inher­ent consti­tu­tional power to use the milit­ary to protect federal prop­erty and func­tions when local govern­ments could not or would not do so. The valid­ity of these claimed author­it­ies has never been tested in court.

What are the weak points in the Posse Comit­atus Act?

Events in 2020 and 2021 have high­lighted two loop­holes in the Posse Comit­atus Act. The first involves the District of Columbia National Guard. Unlike all other state and territ­orial National Guards, the DC Guard is always under pres­id­en­tial control. Despite this, the Depart­ment of Justice has for years asser­ted that the DC Guard can oper­ate in a non-federal, “mili­tia” status, in which it is not covered by the Posse Comit­atus Act. By this inter­pret­a­tion, pres­id­ents can use the DC Guard for law enforce­ment whenever they choose.

Another weak­ness in the Posse Comit­atus Act arises from the law that allows the National Guard to oper­ate in “Title 32 status.” In Title 32 status, a middle ground between purely state oper­a­tions and feder­al­iz­a­tion, Guard person­nel are paid with federal funds and may perform missions reques­ted by the pres­id­ent, but they remain under state command and control. That means they are not subject to the Posse Comit­atus Act, even though they are serving federal interests.

How have these loop­holes in the Posse Comit­atus Act been exploited?

In the summer of 2020, Pres­id­ent Trump deployed the DC National Guard into Wash­ing­ton to police mostly peace­ful protests against law enforce­ment brutal­ity and racism. Simul­tan­eously, over the objec­tions of DC’s mayor, the admin­is­tra­tion asked state governors to deploy their own Guard person­nel into Wash­ing­ton in Title 32 status, and 11 governors did so. Although these out-of-state forces were nomin­ally under their governors’ control, it was later revealed that they were report­ing up through the DC Guard’s chain of command for “coordin­a­tion” purposes. That meant they were ulti­mately taking orders from the pres­id­ent. In this way, the Trump admin­is­tra­tion brought a large, feder­ally controlled milit­ary force into Wash­ing­ton and used it for civil­ian law enforce­ment, all while skip­ping over the proced­ures in the Insur­rec­tion Act and evad­ing the polit­ical costs of invok­ing it. That is exactly what the Posse Comit­atus Act is meant to prevent.

Moreover, the deploy­ment of non-feder­al­ized, out-of-state Guard forces into a juris­dic­tion without its consent repres­ents another threat to the Posse Comit­atus Act. When oper­at­ing in Title 32 status, Guard forces are exempt from the Posse Comit­atus Act because they are under state command and control. A key part of that control is the governor’s right to decline a partic­u­lar federal mission. That right is mean­ing­less if the pres­id­ent can simply approach a differ­ent governor and ask her to deploy her state’s Guard into the unwill­ing governor’s state. In this scen­ario, the cooper­at­ing governor becomes a fig leaf for the pres­id­ent to use the milit­ary as a police force anywhere in the coun­try, free from the constraints of the Posse Comit­atus Act.

How should the Posse Comit­atus Act be reformed?

Congress should pass three reforms to help close these loop­holes in the Posse Comit­atus Act. First, it should trans­fer control over the DC National Guard from the pres­id­ent to the mayor of Wash­ing­ton. The pres­id­ent would still be able to take command of the DC Guard when neces­sary by feder­al­iz­ing it, but it would then be subject to the Posse Comit­atus Act, just like all other feder­ally controlled milit­ary forces.

Second, Congress should clarify that governors may not send their National Guard forces into another state or territ­ory without the latter juris­dic­tion’s consent. This will stop future pres­id­ents who want to use the milit­ary domest­ic­ally, but do not want to follow the laws estab­lished by Congress, from going from governor to governor until they find one who is will­ing to do their dirty work.

Third, Congress should enact a law clari­fy­ing that the Posse Comit­atus Act applies to National Guard forces whenever they report through a federal chain of command, regard­less of whether they have offi­cially been called into federal service. This will ensure that form is not elev­ated over substance and will more fully real­ize the prin­ciple behind the law.