New Draft Article: "Cross-Enforcement of the Fourth Amendment"

The surprising uncertainty when the Fourth Amendment meets federalism.


I recently posted a draft of a new article, Cross-Enforcement of the Fourth Amendment, forthcoming in the Harvard Law Review. Here's the opening:

Imagine you are a state police officer in a state that has decriminalized marijuana possession. You pull over a car for speeding, and you smell marijuana coming from inside the car. Marijuana possession is legal under state law but remains a federal offense. Can you search the car for evidence of the federal crime even though you are a state officer?

Next imagine you are a federal immigration agent driving on a state highway. You spot a van that you have a hunch contains undocumented immigrants. You lack sufficient cause to stop the van to investigate an immigration offense, but you notice that the van is speeding in violation of state traffic law. Can you pull over the van for speeding even though you are a federal agent?

Here's the abstract:

This Article considers whether government agents can conduct searches or seizures to enforce a different government's law. For example, can federal officers make stops based on state traffic violations? Can state police search for evidence of federal immigration crimes? Lower courts are deeply divided on the answers. The Supreme Court's decisions offer little useful guidance because they rest on doctrinal assumptions that the Court has since squarely rejected. The answer to a fundamental question of Fourth Amendment law – who can enforce what law – is remarkably unclear.

After surveying current law and constitutional history, the Article offers a normative proposal to answer this question. Drawing on principles of agency law, it proposes that each government should have the power to control who can enforce its criminal laws. Only those authorized to act as agents of a sovereign should enjoy the privilege of searching and seizing to enforce its laws. The difficult question is identifying authorization: Questions of constitutional structure suggest different defaults for enforcement of federal and state law. Outside the Fourth Amendment, governments can enact statutes that limit how their own officers enforce other laws. The scope of federal power to limit federal enforcement of state law by statute should be broader, however, than the scope of state power to limit state enforcement of federal law.

Comments are particularly welcome in the next week or two, as the editing process has begun and I'll have a chance to make major revisions in the short term that may be harder to make in the longer term. You can send comments to me at okerr [at]

Some readers may remember my post from last May at the old WaPo site about the Second Circuit briefs filed in Marsh v. United States, a 1928 case decided by Learned Hand. At the time, I noted my "mild obsession" with Marsh because of its relevance to my work-in-progress on cross-enforcement. Readers of the new draft will see why: Marsh ends up being an important case.

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  1. No.


    Law enforcement officers are granted certain powers that ordinary citizens do not have, for the limited purpose of enforcing the laws the organ of government has enacted. Beyond that they are ordinary citizens.

    The state trooper has no more authority to enforce marijuana laws than anyone else who is not a federal agent. So he has no right to search the car.

    Similarly, the immigration officer cannot enforce traffic laws. He can’t write a ticket. So he has no authority whatsoever to stop a vehicle for speeding.

    Your solution, as presented, seems plausible, but makes me a bit uneasy. It smells ripe for abuse. I suppose I would ask whether the agent is really empowered to enforce the law, or whether this is a pretext. Are states going to let federal officers and out speeding tickets? Are they going to provide federal agents with whatever training they provide state troopers?

    That’s my decidedly non-legally informed opinion, anyway.

    1. Remember that at least under some circumstances ordinary citizens can make arrests.

      1. I’d like to see evidence of the “citizens arrest” actually existing rather than being a great way to get charges with kidnapping.

      2. Yes.

        But can they conduct searches?

        Can they pull over speeders?

        1. Can [private citizens] pull over speeders?

          I mean, it depends on the state, but yes and no. If speeding is an arrestable crime, as opposed to a mere violation or something, and they personally witness it, then they “can” — in the sense of “may,” that is. (Again, in some states; not all states allow citizen’s arrests for non-felonies.) But they probably can’t in the sense of “able to.” How would a private citizen convince a speeder to pull over?

    2. The exception I’d grant to bernard’s model would be if the state legislature explicitly delegates to federal immigration officers the right to enforce their traffic laws. (And vice versa for federal legislature delegations.)

      And at that point, I think we get most of the way back to Prof Kerr’s proposal – the explicit delegation makes them agents of the other sovereign. Explicit delegation takes most of the judgement and the potential for abuse out of the equation.

      1. Maybe, Rossami, but I’m not so sure it does eliminate the potential for abuse.

        The feds aren’t going to be patrolling the interstates with radar guns, after all, no matter what the state legislature authorizes them to do. Will they have a ticket book? I guess they could, but if not what happens when they pull someone over?

        And will they have marked squad cars with lights and sirens? Will they wear uniforms? If not how does the driver know they are authorized to make a stop?

        So OK. If the state wants to let the feds patrol the highways let them do it the right way.

        My point really is not that I think the idea is bad in the abstract, but that I see a lot of practical problems in implementing it, and I have little confidence state legislatures will deal with the practicalities in a sensible way.

        1. “And will they have marked squad cars with lights and sirens?”

          There are PDs, county sheriff departments and state patrols that used unmarked cars for traffic patrol. They do have lights and usually sirens, but they are concealed in the grill and sometimes the top of the dash where they aren’t readily noticed until activated.

          On the other hand, it’s not like a criminal looking to impersonate a cop can’t fairly readily modify their car in a similar way.

          1. There are PDs, county sheriff departments and state patrols that used unmarked cars for traffic patrol. They do have lights and usually sirens, but they are concealed in the grill and sometimes the top of the dash where they aren’t readily noticed until activated.

            True. Will the feds have similarly equipped cars?

        2. Will they do it well is a question very different from are they allowed to do it at all? I assume that the legislature would make all the appropriate restrictions, training requirements, notifications, etc as part of whatever legislation made the delegation.

          As a general principle, I share your lack of confidence in legislatures. But with our system, there’s really no other choice.

          1. Will they do it well is a question very different from are they allowed to do it at all?

            It is, but maybe if they can’t do it correctly they shouldn’t be allowed to do it at all.

            I assume that the legislature would make all the appropriate restrictions, training requirements, notifications, etc as part of whatever legislation made the delegation.

            I do not share your confidence.

    3. So, a cop pulls someone over for speeding and discovers a stash of counterfeit money. He has to let the guy go? Suppose the guy is wanted for murder in another state?

      1. 1. Cops shouldn’t be using traffic stops to search cars, even for contraband that’s illegal under state/local law.

        2. How did the cop discover the counterfeit money? Are local cops even trained to recognized counterfeit money?

        “Suppose the guy is wanted for murder in another state?”

        Is there an open arrest warrant? A pending extradition request?

        1. If LEO of Entity A cannot enforce the laws of Entity B, how can LEO-A enforce a warrant from Entity B?

          1. This is controlled by state law.

            Since criminal statutes are mostly state law and local LEOs are explictly authorized to enforce state law by state law, generally such warrants are enforceable by any other local jurisdiction within the state under whose law the warrant was issued.

            If A and B are in different states:LEO (A) could still enforce the warrant so if state law in A’s state explicitly authorizes enforcement of out of state warrants.

        2. 1. I agree about pretextual stops. In my hypo, the cop was making a good-faith speeding stop and happened to see the money.

          2. There is an arrest warrant in the other jurisdiction, but no extradition request.

          1. @TwelveInchPianist

            1. It is completely unreasonable that the officer could determine that it is counterfeit without a close examination. This is getting close to the carrying large amounts of cash=probable cause meme that needs to be killed. The officer saw cash, nothing more without a search that would require either probable cause or a warrant.

            2. That would then depend on whether the law in that state explicitly authorizes arrest on the basis of an out of state warrant without an extradition request.

      2. Arrest for speeding (Atwater v. Lago Vista) and contact the Secret Service, issue a summons for speeding and contact the Secret Service, or prosecute for the state equivalent on counterfeit money, which likely exists.

  2. It would be simpler and more textual to eliminate the hair-brained automobile exception.

    1. There is no auto exemption in the constitution. The courts made it up. There were buggies at the time of the 4th Amendment and the constitution makes no exemption for law enforcement to search buggies without a warrant based upon probable cause.

      Everyone should know that the auto stop is an excuse to search for other crimes. Its why police ask a bunch of questions when they stop you rather than just address the offense that they stopped you for like speeding. Why does law enforcement need to know what you do for a living or where you are headed?

      1. Nor does the Constitution authorize suppression for a fourth amendment violation. Judges made it up.

    2. How does that solve the problem, it just pushes the problem to something else. Can Colorado state police get a search warrant to search someone’s home for violating the Fourth Amendment?

  3. The answer would seem very simple. They can, but only if both governments agree. One government controls the laws, the other the agents. Connecting the two requires the agreement of both.

  4. If a place (local, county, state or federal) has law, then any law enforcement officer (local, county state or federal) working in that place can stop the violation of the law and start an investigation.

    #1 There are plenty of other laws besides Federal ones that can justify a search. Decriminalization is very limited. DUI is not legal, marijuana trafficking is not legal.

    #2 Traffic stops are a great resource for law enforcement, and also open to abuse. The officer can only investigate the “hunch” if specific conditions exist after pulling the van over.

    1. Under our constitutional republic, you want to restrict federal officers as much as possible. Just like you want to restrict federal bureaucrats as much as possible. Its why we have the Constitution and the state retain all the power that was not given to the federal government and limited by the Constitution.

      You don’t want federal officers with the power to enforce local ordinances.

    2. #2 Traffic stops are a great resource for law enforcement, and also open to abuse. The officer can only investigate the “hunch” if specific conditions exist after pulling the van over.

      Joe Kennedy, bucking the trend towards marijuana legalization, lamented recently that legalization makes it so much harder for cops to search cars. They can no longer note the smell of marijuana, but must invent some other fake excuse for the search.

      1. Every car in the United States has a broken tail light.

        1. A broken tail light is cause to stop the car and write the driver a ticket. It is not probable cause to search the car.

  5. The answer seems simple enough to me. If the state government wants to allow federal agencies to take part in enforcing its state laws, either the chief of a state police agency, or the legislature acting in the agency’s name, can deputize those federal agents. And the other way around to let state cops enforce federal laws.

    After all, the power of a police agency’s head to deputize people has never been abolished anywhere that I know of, and still gets used surprisingly often.

    This opens up another question which will be controversial. Suppose California’s legislature prohibits its cops from accepting deputized federal power, but one does anyway. What happens, both to him and to anyone he stops for federal violations?

    1. Is deputization normally a long-term proposition, or is it used only for short periods, as an emergency measure?

  6. The Libertarian in me agrees with the no & no comment above.

    The public good aspect can be addressed by the mandate since 9/11 to have a common communication channel (set up for emergencies) between agencies of different levels. That channel can be used to communicate the observed infraction. Should the receiving agency effect a stop, existing precedent suffices.

    If a fed stops for a speeding violation, the 1st Graham factor is, in his mind, satisfied. Not hard to predict how that’s going to go, sooner or later.

    If the sheriff stops to be a border bully, he likely isn’t up to date on the current law.

    We already expect cops to be stunt drivers, medics, psychiatrists & Mother Theresa. Nothing good can come from this.

  7. The federal officers need to ask one question to have probable cause- is speeding off federal property against federal law? Since the answer is no, there is no probable cause to stop a vehicle for speeding.

    State and local police often used minor traffic offenses to search for a wide range of other offenses and anyone who didn’t see this trend was not paying attention. Its why the license plate readers were desired by police departments. They could then just sit on a road and run license plates. If they got a “hit” they considered that probable cause to stop the vehicle. Nevermind that “hits” on license plates might have nothing to do with the current driver currently breaking the law.

  8. Agencies normally comprehend not only authorizations, but also duties and indemnities between principal and agent and extending to third parties. From a quick scan of the article I’m not sure how much of that structure is preserved in this proposal, I’ll take a closer look when time permits.

  9. Surely the Court will just say as long as there is probable cause a crime occurred it’s fine. That is ultimately what the the abortion of a decision Virginia v Moore essentially boils down to. If a state can’t even constrain their own officers then I see no reason they can constrain federal officers. Vice Versa would seem to apply as well.

  10. What’s legal is only tangentially related to what will happen. Cops will be cops; local, state, federal.

  11. This is why Obamacare along with the Fugitive Slave laws light the path to follow to get states to help enforce immigration laws. Give blue states money and more public sector union employees and they will help enforce immigration laws. The “cherry on top” is that Border Patrol is already a majority Latino agency. My advice?make ICE majority black and blue states will embrace ICE and Border Patrol and we will solve this problem!

  12. The more I consider this the less I like it.

    I suspect that, in the case of states authorizing feds to enforce their laws, it will be mostly pretext.

    “Yes, if you see someone speeding and think they might be in violation of immigration laws you can stop them and use our name.”

    That’s really how it will play out, ISTM.

    Whether you think this is a good idea or not, it is unrealistic, I think, to pretend that it will work differently.

  13. Don’t we owe you a beer, Professor Kerr?

  14. Especially after reading this, my default positions are

    1) we need to attract a better class of person to law enforcement

    2) we need to hold law enforcement personnel accountable

    3) law enforcement authority should be restricted or maintained, never expanded, at least so long as points 1 and 2 continue to be a problem

    I leave it to Prof. Kerr to determine whether I owe him more beer. I also leave it to him to get at least 2,000 miles closer to if he wishes to collect.

  15. I feel this question was easier before Virginia v. Moore. Before that case, I saw local cases, attorney motions, etc. where everyone assumed the question was “did the police officer have lawful authority.” They didn’t really distinguish what that authority was. If they had authority, it was fine. If they didn’t, it was a Fourth Amendment violation. Moore seemed to separate things a bit. There’s statutory authority and there’s Fourth Amendment authority and they act completely independently.

    Under Moore, the police may not have lawful authority under Virginia law to arrest someone for not wearing a seatbelt, but they still have Constitutional authority to arrest someone for not wearing a seatbelt and then search them incident to arrest.

    Anyway, as far as recent Constitutional law, Moore seems to be the most relevant case. This discussion would certainly be an extension of Moore. It’s a criminal offense (well, civil infraction) to not wear a seatbelt under Virginia law, but it’s still a violation of Virginia law. The question is whether that can be extended to things that are not violation of Virginia law but still violations of the law committed in Virginia for Fourth Amendment purposes.

  16. Here’s how one state approached the issue: N.J.S.A. 2A:154-5 (the link’s too long) In NJ, specifically defined federal law enforcement officers are authorized to make arrests of 1st, 2nd, or 3rd degree state crimes (felonies, all) about to be committed or attempted in the federal officers’ presence:

    The following persons employed as full-time law enforcement officers by the Federal Government, who are empowered to effect an arrest with or without warrant for violations of the United States Code and who are authorized to carry firearms in the performance of their duties, shall be empowered to act as an officer for the arrest of offenders against the laws of this State where the person reasonably believes that a crime of the first, second or third degree is or is about to be committed or attempted in his presence: [list omitted]

    Note that mere traffic violations are not a 1st, 2nd or 3rd degree crime, but eluding (i.e., leading them on a vehicular chase) can be. Likewise, having a concealed firearm (NJ does not grant carry permits except to a very few well-connected folks) or even a nasty-looking knife is a violation susceptible of being treated as of sufficient degree.

    The statute N.J.S.A. 2A:154-6 gives the US Park Police even more arrest powers (including lower-degree crimes and offenses), but only in limited areas (Liberty State Park, etc.).

  17. Every state (and D.C.) that has legalized marijuana has tightened its law on DUI. A speeding stop with an odor of alcohol or marijuana allows further inquiry into the driver’s possible impairment. If the further inquiry (field sobriety tests, AGN) yields PC for DUI/marijuana then a telephonic warrant for evidence of that crime might be issued, justifying a search of the passenger compartment.

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