I recognized that finding a precise definition of police powers is a bit challenging. But, would it be reasonable to say that police powers are those powers of government reserved to the States by the 10th Amendment?

To what extent that police powers are permitted to Federal government agencies? Are they limited to executive branch agencies? Are they limited to economic issues of interstate commerce?

Does the existence of a statute (2 U.S. Code § 1966 - Protection of Members of Congress) permit the U.S. Capitol Police to exercise police powers throughout the U.S.? How does this statute fit within the concept of enumerated powers of the federal government?

  • Police power is not the same as law enforcement power. Which are you asking about?
    – ohwilleke
    Commented Aug 30, 2021 at 17:44
  • Yes @ohwilleke, that's well established in the answers. Commented Aug 30, 2021 at 19:49

5 Answers 5


I think you're being confused by two separate definitions of "police power." The police power under the 10th Amendment has nothing to do with "the police," i.e. people with guns and badges and uniforms who make arrests. It refers to the authority of a government to make rules for the general welfare. Police power is almost always exercised by the legislature, and when the executive exercises it (e.g. by issuing regulations) it's typically operating under conditions set by the legislature.

The United States has police power in a few situations: DC, federal property and territories, US-flagged ships on the high seas, etc. Outside of those situations, the United States instead has enumerated powers. Congress has a power to tax and spend to promote the general welfare, but otherwise it can only legislate to achieve one of the enumerated powers in the Constitution. Now, courts have read Congress's power to regulate interstate commerce very broadly, but there does need to be some relation to enumerated powers.

You're asking about the Capitol Police, but they don't have "police power" in the 10th Amendment sense. They have the power to carry guns and to arrest people for crimes committed against the United States. This power is limited based on geography and/or the nature of their task; for instance, they have nationwide arrest powers "[i]n the performance of their protective duties," but not when they're traveling outside DC on other official duties (e.g. to attend training).

While there's no litigation I can dig up that's directly on point, courts have repeatedly ruled that Congress has the power to do some not-entirely-legislative tasks in order to protect its own functions. For instance, in Anderson v. Dunn (1821), the Supreme Court upheld an inherent power of the House to hold private citizens in contempt of Congress for disobeying its subpoenas and for the Sergeant at Arms to arrest them and bring them before the House. It seems likely Congress would also have the authority to protect its own members from physical violence. The GAO did an analysis when it was analyzing whether there was a constitutional problem with making Capitol Police IG personnel into special deputy US marshals, and it concluded that there was no issue with congressional employees exercising arrest powers in order to physically protect the legislative branch.

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    What does "IG personnel" mean?
    – phoog
    Commented Aug 29, 2021 at 19:39
  • @phoog Inspector General.
    – cpast
    Commented Aug 29, 2021 at 20:36
  • I certainly may be confused about the 10th amendment and "police powers", so perhaps we need a separate word here, for can you suggest one and update your answer to make the distinction clear? I think that "reserved powers" may be a suitable choice. In that case, I'd certainly agree that these powers are typically declared through state legislation today, though, at the time of the founding fathers, common law may have played a much bigger part. Commented Aug 29, 2021 at 23:11
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    BTW, "police", "policy", "politics", "metropolis", and "polity" all have the same root. Commented Aug 30, 2021 at 2:36
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    @MichaelHardy, probably, but in a different sense than we use it today, and perhaps not in America. For example, Colquhoun, Patrick (1800). Treatise on the Commerce and Police of the River Thames. Some of the early SCOTUS rulings distinguish between "commerce" and "police" without referring to "police power". Commented Aug 30, 2021 at 19:57

"Police power" is not the authority to send people out in blue uniforms with badges and guns to enforce the law. The Supreme Court defines it like this:

The police power of a State embraces such reasonable regulations relating to matters completely within its territory, and not affecting the people of other States, established directly by legislative enactment, as will protect the public health and safety.

Jacobson v. Commonwealth of Massachusetts, 197 U.S. 11 (1905).

This often includes the authority to send out law enforcement with guns, but it also includes all manner of more mundane laws, such as establishing speed limits, building codes, and sewer systems.

In this sense, it is essentially fair to say that the Tenth Amendment reserves the police power to the states, as the federal government is not allowed to just make any law it thinks would be good for the public, though it may do so when they law is within the scope of one of us enumerated powers.

So the federal government may not exercise a general police power" in the technical sense, but there is not really any vertical separation-of-powers issue when it creates a police force like the FBI or ATF, as long as those officers are staying within their jurisdiction and enforcing laws within their grant of authority, which could be to carry out any of the enumerated powers. This could mean addressing issues of interstate commerce, but it could also mean making sure no one besides the government is using currency (Secret Service), or that people are paying their taxes (IRS), or whatever else.

And because the enumerated powers actually belong to Congress, there is no horizontal separation-of-powers issue when Congress creates a police force to protect itself and enforce its own orders.


This page gives an overview of the essential legal issues regarding separation of powers. The peculiarity of the Capitol Police is that it is apparently "under" the legislative branch and not the executive branch, and might be challenged on the same basis as followed in Bowsher v. Synar, 478 U.S. 714 which found that

Congress cannot reserve for itself the power of removal of an officer charged with the execution of the laws except by impeachment...

The structure of the Constitution does not permit Congress to execute the laws; it follows that Congress cannot grant to an officer under its control what it does not possess

The Capitol Police statutorily reduces to the Capitol Police Board and whoever they hire and fire. The interesting thing is that there is apparently nowhere in the US Code that says where that board comes from. §1901 was amended to strike that specification, previously including “, the members of which shall be appointed by the Sergeants-at-Arms of the two Houses and the Architect of the Capitol Extension”. The two houses have the authority to set their own rules, so they can select (and fire) their respective Sergeants-at-Arms (since the Capitol building is where the legislature does its business). However, the Architect of the Capitol is appointed by POTUS, with the advice and consent of the Senate. It thus seems extremely unlikely that a separation of powers challenge to the constitutionality of the CPB would be successful. Separation of powers seems to be a dead end.

Enumerated powers is a different argument, since Congress has assumed numerous powers that don't seem to be clearly assigned to the federal government. Congress can pass a law protecting the members of Congress and the members of their family, and they can pass a law authorizing the Capitol Police to perform such protections, just as they can pass a law enabling the Secret Service to protect POTUS, even when he is not in the Whitehouse.


would it be reasonable to say that police powers are those powers of government reserved to the States by the 10th Amendment?

Not particularly. Police power is most commonly associated with the power of the executive to use physical force to enforce criminal law. This is subject to separation of powers because the law is established by the legislature (either with executive assent or by a supermajority) and because punishment of violations is decided by the judiciary after an adversarial trial in which the executive must prove its case while the defendant is given the opportunity to discredit the executive's case.

In general, any government that enforces a criminal code will need a police force for that purpose. The tenth amendment might reserve certain areas of criminal enforcement to the states, but it does not reserve all police power to the states. If it did, how would the federal government enforce criminal law in the areas that it has pre-empted from the states, such as immigration?

The judiciary and the legislature also have the power to use force, albeit in more limited circumstances than the executive. Judicial bailiffs and legislative sergeants at arms uncontroversially use force to maintain order in courtrooms and legislative chambers. Bailiffs may also enforce court orders outside the courtroom, at least in some jurisdictions. Whether this is considered "police power" largely depends on your definition of "police power," and whether the capitol police have the power to do something away from the capitol is probably not dependent on whether that act falls within any particular definition of the term "police power."

The interstate commerce clause has seen some very broad use over the years, so an issue need not be obviously economic or commercial in nature to implicate the interstate commerce clause. As far as I understand the issues pertaining to the capitol police, the point of their operations outside of Washington DC is to cast a wider net in undertaking their mission to protect congress. The extent to which that is constitutional certainly may be questioned, and I am sure it will be if they bring charges against someone through such an operation, but no court is going to find that the capitol police had acted beyond its authority in investigating or apprehending someone suspected of plotting to blow up the capitol simply because the person is in some distant state.

It is also difficult to imagine that a court would find the statute cited in the question to be unconstitutional simply because the officers it empowers to make arrests have a chain of command that leads to the authority of congress rather than to the executive. Furthermore, if a court did make such a finding, it wouldn't take much to reorganize the capitol police as an executive force with a mission of protecting congress under the operational command of the sergeants at arms.

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    This answer completely misunderstands the meaning of "police power."
    – bdb484
    Commented Aug 29, 2021 at 23:52
  • @bdb484 yes, cpast covered that very well.
    – phoog
    Commented Aug 29, 2021 at 23:54
  • 1
    Why not correct the answer?
    – bdb484
    Commented Aug 30, 2021 at 0:14
  • @bdb484, note that my question was about "police powers" plural, not the "police power of the state". My own research suggests that the singular term's constitutional (10th amendment) sense may be archaic. I certainly wouldn't see it as a reason to downvote phoog's answer. Commented Aug 30, 2021 at 0:54
  • @Burt I would and do. The two senses of "police" are perhaps unfortunate, but US constitutional law continuities to use the older and broader sense. Commented Aug 30, 2021 at 0:57

With the benefit of other answers pointing out the difference between police power in a constitutional context and the interpretation frequently inferred in less-legalistic contexts, I have found a rather precise definition of traditional police power from SCOTUS:

The States' traditional police power is defined as the authority to provide for the public health, safety, and morals, and such a basis for legislation has been upheld. See, e.g., Paris Adult Theatre I v. Slaton, 413 U. S. 49, 413 U. S. 61. -- Barnes v. Glen Theatre, Inc., 501 U.S. 560 (1991)

Given that SCOTUS is labeling this definition as "traditional" police power, it seemed relevant to search for references to "modern police power". This has proved more challenging. It certainly seems clear that Canadian english viewpoint on "police power" differs substantially from SCOTUS's, e.g. Chief of London Police rejects new police powers enforced by Ont. government

  • 2
    I think “traditional police power” there parses as “the police power that states traditionally have,” not as some unique thing. If you want to search for the power to enforce laws, arrest power might be a better term to use. That said, the basic issue is that “police power” has a specialized legal meaning that’s different from the plain English meaning, and I’m not sure there’s a great way around that.
    – cpast
    Commented Aug 30, 2021 at 13:02

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