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Anthony Amsterdam’s article, Perspectives On The Fourth Amendment is one of the best, if not the best, law review article written on the Fourth Amendment. Thus, Minnesota Law Review on its hundredth anniversary fittingly recognizes and honors Professor Amsterdam’s article in its Symposium edition, “Standing on the Shoulders of Giants: Celebrating 100 Volumes of the Minnesota Law Review.” I am flattered that the Law Review invited me to participate in this Symposium. Specifically, my article connects two perspectives from Amsterdam’s article — the Fourth Amendment’s concern with discretionary police power and the Framers’ vision of the Fourth Amendment to bar arbitrary and ruleless searches and seizures — to an aspect of modern American society that affects millions of people: traffic stops by the police. This past Term, the Supreme Court decided Rodriguez v. United States. At issue was whether the Fourth Amendment “tolerates a dog sniff conducted after the completion of a traffic stop.” The Court, in a 6-3 ruling, held that “a police stop exceeding the time needed to handle the matter for which the stop was made” violates the Fourth Amendment. While certainly a temporary victory for Mr. Rodriguez, I submit that Rodriguez is a vexing decision on several fronts. As I will explain, Rodriguez is a significant ruling because it rejects the argument that police can prolong a traffic stop to pursue a drug investigation. At the same time, however, Rodriguez blesses two troublesome investigative techniques that have been utilized in the country’s seemingly never-ending “War on Drugs” and that are, in my view, inconsistent with Fourth Amendment freedoms and contrary to Professor Amsterdam’s insights on the amendment. Rodriguez v. United States explained that the Fourth Amendment tolerates certain unrelated investigations that do not lengthen a roadside detention. Rodriguez’s endorsement of police questioning was unnecessary and regrettable. It was gratuitous because the issue before the Court — whether police can detain a motorist to use a drug-sniffing canine after the completion of a traffic stop — had nothing to do with unrelated questioning during a traffic stop. The Court’s comments were lamentable for two reasons. First, the practice of questioning motorists about matters unrelated to the traffic stop is inconsistent with the same legal framework the Court relied upon to invalidate the detention and dog sniff at issue in Rodriguez. Second, there was no reason for the Court to provide its imprimatur on a criminal investigative technique that police regularly use to arbitrarily interrogate motorists during routine traffic stops. On a deeper level, Rodriguez’s dicta about police questioning during traffic stops is disappointing for its failure to appreciate the fundamental value of the Fourth Amendment. As Professor Amsterdam has taught us, “the fourth amendment is quintessentially a regulation of the police – that, in enforcing the fourth amendment, courts must police the police.” More specifically, Professor Amsterdam’s article teaches that controlling the discretionary power of officers while they are effectuating searches and seizures is essential to protecting Fourth Amendment freedoms. Police seize millions of Americans every year during traffic stops. Traffic stops are rife with the potential for arbitrary and discriminatory police power. “Once an officer stops a motorist for a traffic offense, the officer has the discretion to transform that traffic stop into an investigation of other serious crimes without the check of reasonable suspicion or probable cause.” If the Justices want to protect the Fourth Amendment rights of millions of American motorists, they should recognize that police interrogation of motorists about subjects unrelated to the reason for the traffic stop provides police with unchecked discretion to pursue a criminal investigation and is beyond the scope of an ordinary traffic stop. This Article proceeds in two parts. Part I explains the result and legal reasoning of Rodriguez. It also explains the legal standard, first announced in 1968, that courts have traditionally used to judge the constitutionality of police conduct during investigative detentions, which includes traffic stops. Part II discusses recent rulings of the Court that have been read to authorize police to pursue criminal investigative practices – such as dog sniffs and interrogation unrelated to the reason for the stop – during ordinary traffic stops, provided those practices do not prolong the traffic stop. Part II also explains why those rulings – Illinois v. Caballes, Muehler v. Mena, and Arizona v. Johnson – have been misread and misapplied to allow arbitrary police interrogation during routine traffic stops.