A 1981 Supreme Court decision allows the warrantless search of a car's interior at the time of a driver's arrest to protect the police from concealed weapons. For the sake of simplicity, the Court allows the search even if the driver is not in a position to reach a weapon -- even when the driver has been removed from the car and handcuffed.

Thornton's case pushes the limits of that holding. Thornton was not responding to police action when he parked and left his car. When he encounters the officer, he's a pedestrian who happens to be in the vicinity of his car. If Thornton had been walking near his car (but not driving) when the officer first saw him, the officer wouldn't be allowed to search the car without probable cause to believe it contained evidence of a crime. Why should this case be different?

The Court has long believed that mobility and visibility make cars less entitled to privacy protection than houses or hotel rooms. But allowing a search of Thornton's car would end the "bright line" rule that the Court desired. What if the officer loses sight of the driver for a few minutes, then spots him standing a block from his car? What if the driver is three blocks from his car? What if the officer saw the driver exit his car but waited an hour before arresting him? If the Court wants to adhere to a "bright line" rule, it must accept the fact that the rule might occasionally benefit the defense.

If the Court is looking for one, there's a coward's way out. The Court recently said that the police usually have probable cause to believe that everyone in a car is guilty of a crime if none of the occupants admit ownership of concealed drugs. Why is it probable that everyone in a car knows about hidden drugs? Because the Court said so. Using that same logic, the Court may say the officer had probable cause to believe that the car contained evidence of a crime because Thornton had drugs in his pocket and had just exited the car.