Mumford v. Iowa Will Complicate or Clarify the Rules for Dog Sniff Cases

Noah Brozinsky has been a civil and criminal law litigator since 2013. From 2018-2021 he supervised dozens of new lawyers at the Miami Public Defender’s Office, teaching criminal trial jury selection, trial advocacy, and advanced Fourth Amendment topics. Before joining Kaiser PLLC, Noah was an Assistant Counsel and National Negotiator with the National Treasury Employees Union. He now represents both plaintiffs and defendants in cases involving the federal government.

In April 2025, the Supreme Court docketed Mumford v. Iowa, a case asking whether a police dog’s sniff of the interior of a lawfully stopped vehicle violates the Fourth Amendment if there’s neither consent to search the car nor probable cause to believe the vehicle contains drugs.

In March 2022, Ashlee Mumford was pulled over for a minor traffic infraction—two numbers on her license plate were covered in dirt.  The officers called for a K9 unit to sniff the outside of the car, but the dog stood on its hind legs and its nose crossed the plane of the passenger window.  The dog then alerted to the presence of narcotics inside the car.  The police searched the car, ultimately charging Ms. Mumford with possession of methamphetamine, marijuana, and a pipe.  After a suppression motion was denied, she was convicted of marijuana possession and possessing drug paraphernalia (she was acquitted of the meth charge).

This is a straightforward story, but there’s a lot going on here in terms of Fourth Amendment law and history.

Dog sniff cases are an important and evolving area of the law with implications for future Constitutional questions at the intersection of technology, privacy, and property rights far beyond issues relating to the reliability of the dogs themselves.  The Supreme Court has held that, generally, the use of drug-sniffing dogs does not offend the Constitution because there’s no right to privacy in contraband.  “[A] dog sniff conducted during a concededly lawful traffic stop that reveals no information other than the location of a substance that no individual has any right to possess does not violate the Fourth Amendment.”  Illinois v. Caballes, 543 U.S. 405, 410 (2005).  The Supreme Court has also ruled that police can’t take a drug-sniffing dog onto one’s curtilage for a warrantless search because that’s a physical invasion of a Constitutionally protected space.  Florida v. Jardines, 569 U.S. 1, 7 (2013).

What the Court has not ruled on, and what Mumford concerns, is whether a dog sniff that exceeds Caballes in a de minimus way violates a Fourth Amendment privacy interest and/or property interest.  The subtextual question is: just how big of a deal is it if the dog enters the car for a closer sniff?

Some background on dog sniff cases at the Supreme Court helps frame the issues at stake in this case:

• Was the car lawfully seized? Even a traffic infraction as minor or unoffensive as dirt covering a tag is Constitutional license enough for a police officer to effect a traffic stop without violating the Fourth Amendment.
• Did the officers have the right to detain Ms. Mumford and her car for the dog sniff? Maybe … and probably. As long as there is reasonable suspicion of drug possession and no “undue delay” the police can call for a K9 unit to search the exterior of a car.  The issue is whether the waiting period for the dog to arrive unjustifiably prolongs the stop longer than necessary to effect the purpose of enforcing the traffic violation.
• Once the dog arrives at the scene, what can the police use it for? Caballes held that the police may sniff around the outside of the car because such a process does not invade any Fourth Amendment privacy interest. No one has a “right” to possess contraband, so a search that only reveals the presence or absence of that contraband isn’t really a search at all. There’s no need for reasonable suspicion, let alone probable cause.  Dog sniffs are a sui generis facet of law enforcement, and there’s no Fourth Amendment foul. (So said a majority of the Court in Caballes, anyway).
• If the dog is outside the car and alerts to the presence of drugs inside the car, how should the police proceed? A dog’s “alert” to the presence of drugs in the car is probable cause for a search of the car. Florida v. Harris, 568 U.S. 237 (2013) holds that a trial court must employ a totality-of-the-circumstances approach when adjudicating a challenge to the officer’s interpretation of the dog’s actions.  There is no hard-and-fast rule, but defendants have a right to demand a suppression hearing where they can challenge whether the dog was adequately trained, whether the dog acted in accordance with its training, whether the police officer was qualified to interpret the dog’s actions, and whether there are any other facets of the case that would suggest the dog was acting outside its training.

So, it would seem like Ms. Mumford’s case is straightforward: The car was seized lawfully; there was presumably reasonable suspicion of drug possession and no undue delay; and the use of the dog was lawful.  What’s different here?

What’s different is that the dog poked its snout inside the car before alerting.  The Court could very well rule this was a trespass akin to the impermissible trolling for evidence along a curtilage in Jardines.  As in Jardines, the Court noted that the privacy interest at issue (the possession of contraband) is secondary to the more burdensome tort—the physical invasion—that occurs when the government exceeds its license to enter a given space.

On the other hand, the Court may note that cars are less protected than homes when it comes to warrantless searches.  The Automobile Exception holds, generally, that there’s less Fourth Amendment protection in moveable vessels along the road, and therefore a de minimus intrusion such as occurred here is not afoul of any Fourth Amendment interest.  Since the police needed only probable cause to search the car in the first place, the errant dog’s sniff as part of a lawful procedure was less offensive than, say, if a policeman was walking a dog down the street and the dog bolted toward someone’s front door.

No matter how the Court rules, this case could have big implications for search-and-seizure cases carrying forward.  The Court may consider that the officers shirked their responsibility to ensure the dog didn’t exceed the scope of the search.  The Court may consider, on the other hand, that Harris allows for a totality-of-the-circumstances approach and therefore consider that a sniff through the window was instinctual and not subject to suppression.

And, these cases are far more important than dogs sniffing for drugs.  The idea that the government can search for contraband without a warrant because a person doesn’t have the right to possess that contraband in the first place is unnerving (and circular).  Caballes—which holds that dog sniffs require neither probable cause nor reasonable suspicion because the search is sui generis and binary—should be considered a narrow ruling applicable only to dogs’ use in lawful traffic stops.  Its application to remote searches of say, cell phones and hard drives, should be avoided.

The Court can make clear in Mumford that Caballes is also limited to exterior sweeps outside the car.  More importantly the Court can make clear that the dog sniff cases are limited to dogs and should not be analogized to as yet unimagined technologies.