Assume you are a 17-year-old licensed driver and your father's driver's license has been suspended. He hands you the keys to his car and asks you to run an errand. While completing that errand you are stopped by the police. You have not broken a single law. You were stopped only because the officer guessed that your father might be driving. Was the traffic stop lawful?

The above scenario is hypothetical, but the questions it raises are genuine. In November, the U.S. Supreme Court heard oral arguments in a case that asks whether the Fourth Amendment "always permits a police officer to seize a motorist when the only thing the police officer knows is that the motorist is driving a vehicle registered to someone whose license has been revoked."

The case is Kansas v. Glover. In 2016, a patrolling sheriff's deputy ran the plates on a Chevrolet pickup truck and learned that the truck's owner, Charles Glover, had a revoked driver's license. The deputy had no idea if Glover was actually behind the wheel. But the deputy still pulled the truck over on the assumption that Glover was driving. He was. Now Glover wants the Supreme Court to rule the stop unconstitutional.

"When a driver loses his license, he and his family must rely on other drivers (a spouse, a driving-age child, a child-care provider, a neighbor) to meet the family's needs," Glover and his lawyers point out in their brief to the Supreme Court. "Under Kansas's proposed rule…any of those other drivers can be pulled to the side of the road at any moment merely for driving a lawfully registered and insured car in a completely lawful manner." That rule, they argue, is an "unjustified intrusion on personal privacy" that violates the Fourth Amendment.

According to Kansas, it does not matter if innocent drivers happen to get stopped based on the false assumption that someone else is behind the wheel. "While it is certainly possible that the registered owner of a vehicle is not the driver, 'it is reasonable for an officer to suspect that the owner is driving the vehicle, absent other circumstances that demonstrate the owner is not driving,'" the state maintains. "That is the very point of investigative stops—to confirm or dispel an officer's suspicion."

The Supreme Court has an unfortunate record of sometimes whittling away the Fourth Amendment in traffic stop cases. A victory for the state here would lower the constitutional safeguard even further.