The Fourth Amendment protects people from unreasonable searches and seizures by the government — or that’s how it works in theory, anyway.

In practice, though, court decisions over several decades have created so many exceptions to this constitutional principle as to render it effectively meaningless in many real-world situations.

On Monday, the Supreme Court further weakened the Fourth Amendment by making it even easier for law enforcement to evade its requirement that stops be based on reasonable suspicion. The justices ruled 5 to 3 that a police officer’s illegal stop of a man on the street did not prevent evidence obtained from a search connected to that stop to be used against him.

The case, Utah v. Strieff, started when the police in Salt Lake City got an anonymous tip of drug activity at a house. An officer monitoring the house became suspicious at the number of people he saw entering and leaving. When one of those people, Edward Strieff, left to walk to a nearby convenience store, the officer stopped him and asked for his identification. A routine check revealed that Mr. Strieff had an outstanding “small traffic warrant.” The officer arrested him based on that earlier warrant, searched him and found drugs in his pockets.