When officers stop a car for a traffic violation, they may employ a trained dog to sniff the vehicle for drugs. But how long may they prolong the stop for the sniff? Can they even prolong it at all?On Oct. 2, the U.S. Supreme Court granted review in a case that raises these questions. Dennys Rodriguez v. United States, 13-9972, involves a general scenario that recurs around the country, in which a traffic stop is extended for a dog sniff. How the justices view this case may depend upon whether they have a formalist or functionalist view of the Fourth Amendment. In Rodriguez, Officer Morgan Struble, patrolling a Nebraska highway around midnight with his canine Floyd in the car, observed Dennys Rodriguez's vehicle veer onto the shoulder of the highway and jerk back onto the road. Struble stopped Rodriguez and his passenger. The officer gathered Rodriguez's license, registration and proof of insurance; ran a record check on Rodriguez; questioned both occupants; and then returned the documents to Rodriguez with a written warning. During that process, Struble called for a backup officer to ensure his safety while he led Floyd around the vehicle. Rodriguez denied consent for that dog sniff. After giving the written warning, Struble directed Rodriguez out of the vehicle to wait for the second officer to arrive, which took a few minutes. Floyd alerted as Struble walked him around the car, and a search of Rodriguez's car revealed methamphetamine, leading to his federal prosecution. The stop was prolonged seven or eight minutes from the time that Struble wrote the warning to the time that Floyd alerted. (Typically, in other cases, the sniff is delayed while one officer awaits another's arrival with the dog.) Rodriguez claimed that this delay violated his Fourth Amendment right to be free from unreasonable seizures. Applying its established law, the 8th U.S. Circuit Court of Appeals recognized that a dog sniff may work an unconstitutional seizure if it "unreasonably prolongs" a traffic stop, but held that a "brief delay" to employ a dog does not unreasonably prolong the stop. The court thus held that the seven- to eight-minute delay constituted a "de minimis" intrusion on Rodriguez's liberty, citing several cases where it had upheld dog-sniff delays of less than ten minutes. The 8th Circuit's approach is similar to that in California and much of the country following Illinois v. Caballes, 543 U.S. 405 (2005). In that case, the Supreme Court held that a dog sniff of an exterior of a vehicle during a traffic stop does not violate the Fourth Amendment. But Caballes involved a sniff that occurred during the traffic stop itself. The court noted that "a seizure ... can become unlawful if it is prolonged beyond the time reasonably required to complete that mission." The court provided no guidance as to when that would happen, though it cited a case in which the officer called a canine unit that took fifteen minutes to arrive as an example of an unreasonably prolonged search. See People v. Cox, 782 N.E.2d 275, 277 (Ill. 2002). Since Caballes, long traffic-stop delays due to dog sniffs have been held unconstitutional. For example, California courts have held a delay of over an hour too prolonged, People v. Gomez, 117 Cal. App. 4th 131 (2004), and the 9th U.S. Circuit Court of Appeals has ruled a 30-minute delay too great, United States v. Motley, 344 Fed. Appx. 445 (2009). On the other hand, our appellate courts uphold de minimis delays. See, e.g., People v. Chan, 2013 WL 6843598 (Cal. App. 2013) (five-minute delay); People v. Simon, 2013 WL 5476837 (Cal. App. 2013) (one- to two-minute delay); United States v. Brown, 222 Fed. Appx. 652 (9th Cir. 2007) (delay of "minute or two"). The de minimis approach is common enough around the country that, in his leading treatise, Professor Wayne R. LaFave cites various cases and observes: "[P]recisely because the dog sniff itself takes so little time, courts in this context have been especially willing to employ a 'fudge factor' regarding the temporal limits of the traffic stop; if the dog sniff is conducted immediately or soon after completion of those tasks actually connected with the traffic violation, the resulting additional custody is deemed so de minimis as to be of no consequence." "Search and Seizure: a Treatise on the Fourth Amendment," Section 9.3(f). In Rodriguez, the defendant's petition for a writ of certiorari urged the Supreme Court to take the case to hold that even de minimis extensions of a traffic stop for a dog sniff are unwarranted. When the traffic stop has ended, he argued, "officers are initiating a new seizure when they seek to conduct a canine sniff." This is a formalistic view of the Fourth Amendment, as it posits that the moment that a citizen's papers are returned following a citation (or warning) any further detention of the suspect is constitutionally invalid. The Supreme Court has not clearly settled whether a new seizure occurs when a subject is kept past the time his license is returned. See Ohio v. Robinette, 519 U.S. 33 (1976) (holding that the Fourth Amendment does not require that a lawfully seized person be advised he is "free to go" when his license is returned but stating that that voluntariness of consent after that point is determined from all the circumstances). In contrast, the government's opposition to certiorari raises practical, functionalist arguments. If Struble had Floyd perform the sniff without waiting for Struble's backup to arrive - or if two officers had been in Struble's vehicle rather than one - the same sniff would have occurred earlier and have been permitted by Caballes. The government thus argued that allowing the stop extended "is consistent with common sense - the fact that the sniff was conducted shortly after, instead of during, the issuance of the warning did not change what the sniff itself would or would not reveal, nor did it subject petitioner's vehicle or personal effects to any greater intrusion." If the dog had not alerted, the government pointed out, the defendant would be free to proceed with his travel plans hardly affected by the brief extension. It also seems plausible that, if de minimis extensions were unavailable, an officer in Struble's position could take a bit of additional time before writing a ticket to ensure that the dog sniff occurred during the stop. (Caballes stated that the sniff must occur during the time "reasonably required" for the traffic stop, not the time the stop actually takes.) These are functionalist arguments as to why de minimis extensions of a traffic stop for a dog sniff are not constitutionally unreasonable. It is worth noting that Rodriguez will not address the situation where an officer develops suspicion of drug activity during a traffic stop and that suspicion justifies prolonging the stop for a dog sniff. The government argued alternatively in lower courts that Struble developed such suspicion, but that argument was neither addressed by the Eighth Circuit nor raised by the certiorari petition; if Rodriguez prevails, the case presumably will be remanded for the appellate court to address that argument. Rodriguez should, however, resolve whether an officer can briefly prolong a traffic stop to conduct a dog sniff absent particularized suspicion of narcotics. It may be interesting to observe how the court views the interplay between formalistic and functionalist arguments as to what the Fourth Amendment requires.