Whren v. United States

Plainclothes officers, already suspicious that a drug deal was underway, pulled over a car after observing an unsignaled turn and speeding. Approaching the car, they saw Whren (defendant), a passenger, holding plastic bags of cocaine, and he and the driver were arrested and convicted after the trial court admitted the drugs over Whren's objection; the court of appeals affirmed.

Whether the Fourth Amendment is violated when an officer has probable cause that a traffic violation occurred but his primary motive for the stop is unrelated to traffic enforcement.