In Rodriguez v. United States, the Supreme Court ruled on a case involving an individual's Fourth Amendment rights during a traffic stop. The petitioner, Dennys Rodriguez, was pulled over for driving erratically and issued with a warning. However, the officer then detained him without reasonable suspicion in order to conduct a dog sniff test around his vehicle which resulted in finding methamphetamine. Rodriguez argued that this detention violated his Fourth Amendment right against unreasonable searches and seizures as it extended beyond the time needed to handle the matter for which he was stopped (the traffic violation). In its decision, the Supreme Court agreed with Rodriguez by ruling 6-3 that police officers cannot extend an otherwise completed traffic stop for any period of time without reasonable suspicion necessary to justify detaining an individual beyond completion of their original purpose - even if only few minutes are involved.

In the dissenting opinion for Rodriguez v. United States, Justice William Brennan disagreed with the majority's ruling that a dog sniff of a vehicle during a lawful traffic stop did not constitute as an unreasonable search under the Fourth Amendment. He argued that this decision ignored previous rulings which established that people have a reasonable expectation of privacy in their personal belongings and effects, even when they are inside vehicles. Furthermore, he contended that allowing such searches without any suspicion of criminal activity would give law enforcement too much discretion to invade individuals' privacy rights arbitrarily or discriminatorily. Justice Brennan also expressed concern about potential abuses of power by police officers who might use routine traffic stops as pretexts for conducting warrantless drug investigations based on hunches rather than concrete evidence.