The Posse Comitatus Act of 1878 was enacted to keep the U.S. military out of civilian law enforcement except where authorized by Congress. While it is meant to prevent federal troops from being used against Americans, gaping loopholes and exceptions threaten to swallow the rule. Brennan Center counsel Joseph Nunn discusses his new report covering the reforms needed to strengthen this crucial guardrail.
What is the origin of the phrase posse comitatus, and how does that relate to the purpose of the Posse Comitatus Act?
That is actually a fun fact. Posse comitatus is Latin for “the power of the county.” It refers to the authority that sheriffs and some other law enforcement officials had at common law to gather a group of citizens to pursue lawbreakers. In Britain and the United States, before the modern era, the sheriff was often the only local law enforcement officer, and any significant lawbreaking would be more than he could handle alone. The posse comitatus power allowed him to call in reinforcements. To connect this to popular culture, in a Western film, when the sheriff gathers a “posse” of townsfolk to chase outlaws, that’s a posse comitatus.
The Posse Comitatus Act is so named because it prohibits the use of federal armed forces as a posse comitatus or to otherwise enforce the law unless doing so is expressly authorized by Congress.
What is the main issue with the Posse Comitatus Act as it’s written now?
It’s too weak. The Brennan Center’s Liberty and National Security Program is often concerned with statutes that are dangerous because they grant too much authority or they’re too broad. The Posse Comitatus Act, however, is dangerous because it doesn’t go far enough: it’s too flimsy a guardrail. On paper, the law limits federal military participation in law enforcement, but it is undermined by an overabundance of exceptions, significant loopholes, and the lack of an effective enforcement mechanism.
As a result, the principle enshrined in the Posse Comitatus Act is protected more by norms and historical practice than by the text of the law itself. Unfortunately, we’ve entered an era in which we can no longer rely on tradition to constrain executive action.
What exceptions and loopholes in the Posse Comitatus Act concern you the most?
When thinking about weak points in the Posse Comitatus Act, the Insurrection Act is the 800-pound gorilla in the room. This law grants the president incredibly broad authority to deploy the military domestically, under circumstances that aren’t clearly defined. The Brennan Center has written extensively about the dangers of the Insurrection Act and proposed reforms, so our new report focuses on the lesser-known loopholes.
One significant loophole is the District of Columbia National Guard. While all other National Guards are commanded by their state or territorial governors, the DC Guard falls under the president’s direct control at all times. Although it can act as a federal force, the Department of Justice has long claimed it can also operate as a non-federal “militia” that is not constrained by the Posse Comitatus Act. This means presidents can theoretically use the DC Guard for law enforcement whenever they choose.
Another loophole is Section 502(f) of Title 32 of the U.S. Code, which allows the National Guard to carry out federal missions at the request of the president or secretary of defense while remaining under state control, thus bypassing the Posse Comitatus Act. While the rest of Section 502 is principally used for training missions, there are no criteria limiting what kinds of missions Subsection f can be used for. The Trump administration exploited this license a few years ago when it invited National Guard troops from 11 states into DC to suppress protests following the murder of George Floyd. This unprecedented action was done without invoking the Insurrection Act, as the president could simply ask sympathetic state governors to give the orders on his behalf.
To make matters worse, the Posse Comitatus Act lacks an effective enforcement mechanism. The law is a criminal statute, yet there’s no real threat of prosecution for violating it in practice. No one has ever been convicted for violating the Posse Comitatus Act, and only two people have ever been prosecuted — both more than 140 years ago.
Why is it a problem for the military to act as a domestic police force?
Military participation in law enforcement is sometimes necessary in a true crisis, but it is always risky. One of the most immediate concerns is that soldiers are trained to fight an enemy who lacks constitutional rights; they are not generally trained for domestic law enforcement. For instance, soldiers aren’t necessarily instructed in how to provide due process or conduct searches and arrests appropriately. Asking soldiers to perform these duties raises the risk of infringing on the public’s First, Fourth, and Fifth Amendment rights — and it is unfair to the soldiers, who did not enter the military with the goal of policing their fellow citizens.
Beyond those immediate concerns, there’s an American tradition that traces back to the founding of this country rejecting military interference in civilian affairs. The founders were extraordinarily suspicious of military power, and not just when it was used domestically. During the Constitutional Convention, there was significant debate about whether to even allow a national standing army. These debates were motivated by fears that such an army could easily become a tool of tyranny. When an army is turned inward, that danger is particularly acute.
Importantly, though, the Brennan Center’s stance is not that military participation in law enforcement is never appropriate. Rather, it should be confined to emergencies when civilian authorities are truly overwhelmed. The January 6 insurrection is a paradigmatic example of this. Civilian authorities — the Capitol Police — were manifestly overwhelmed. And in that moment, there was a genuine physical threat to Congress. So in that case, deployment of the DC National Guard was entirely appropriate. Indeed, the president rightly came under criticism for delaying deployment of the Guard.
Why is prosecution under this law so rare?
The most straightforward answer is that violations are not very common. Federal forces aren’t deployed domestically very often, and when they are, they are guided by strong norms of compliance — at least historically speaking. Our report aims to highlight the significant risk of abuse and misconduct rather than to identify a clearly established pattern of it.
There are likely other reasons at play too. For instance, one-off infringements by individual soldiers acting without authorization might be considered too minor to justify criminal charges, while there would be little appetite within the Department of Justice to pursue criminal charges against a soldier acting on orders passed down from civilian commanders.
If the law is so problematic, why hasn’t it been reformed before?
There are a few reasons. Chief among them is that this is an area of the law that Congress is extremely reluctant to touch. The Posse Comitatus Act is regarded as sacrosanct. Lawmakers are wary of making changes to such an important guardrail — but that’s why it’s important to show that the guardrail isn’t as solid as they might think.
Another reason is that significant violations of the Posse Comitatus Act are not common, as I mentioned before, in part because the military takes compliance very seriously. This stems, I believe, from a commitment to the principle enshrined in the law, as well as the more practical reason that the military does not like to do domestic law enforcement. From their perspective, it’s not their job. They understand it’s not something they’re principally trained for, it is a distraction from what they regard as their core focuses, and it is unpopular with both soldiers and the public.
The small number of violations can also be chalked up to the United States being very lucky so far. Presidents have generally acted with restraint when it comes to domestic use of the military, but there’s no reason to assume that will remain true. Luck is no substitute for robust legal safeguards.
What are the main reforms you’re advocating for?
There are several important reforms outlined in the report, but I’ll mention four particularly important ones here. First and foremost, reform the Insurrection Act. There must be clear standards for when and how presidents can use the law, as well as meaningful checks by the other branches of government.
Second, close the DC National Guard loophole by either transferring control over the DC Guard to the mayor of Washington or extending the Posse Comitatus Act to cover the DC Guard at all times.
Third, close the Section 502(f) loophole. The Posse Comitatus Act should be extended to cover National Guard deployments when the Guard performs a federal mission at the request of the president or the secretary of defense.
Fourth, create more effective enforcement mechanisms. Congress should impose an exclusionary rule that prevents evidence obtained in violation of the Posse Comitatus Act from being used in court. Congress should also consider allowing individuals harmed by violations of the Posse Comitatus Act to sue for civil damages. The risk of having crucial evidence thrown out and the potential for lawsuits by injured citizens will provide far stronger incentives for both the military and their civilian leadership to comply with the law than the nonexistent prospect of criminal prosecution.
What are the prospects for reforming the Posse Comitatus Act?
There is a bipartisan understanding in Congress that some degree of domestic deployment reform is necessary, particularly regarding the Insurrection Act. Additionally, there is some support for broader reforms aimed at the National Guard and the Posse Comitatus Act. That said, advancing these reforms will take time and require a good deal of discussion about why they matter, as this area of law is not tremendously well understood. Our hope is that this report can help to move this process forward.
