The court heard a case from Kansas that could have a big impact on when police may stop a motorist who has not otherwise broken the law, sorting through phrases such as "common sense" (18 mentions), "reasonable suspicion" (44 mentions) and "assume" and "assumption" (25 mentions).
Kansas Solicitor General Toby Crouse said it was "common sense" for sheriff's deputy Mark Mehrer to stop a truck owned by Charles Glover after a routine license plate check showed that Glover had a suspended license.
"It would have been poor police work for Deputy Mehrer not to initiate the stop in this case and investigate further to confirm or dispel his suspicion," Crouse said.
Justice Department lawyer Michael Huston agreed. "The purpose of reasonable suspicion is simply to conduct further investigation," Huston told the court.
But what if a law-abiding citizen was simply borrowing the truck? "There's literally nothing she could do to avoid being seized," said lawyer Sarah Harrington, representing Glover.
Glover was driving near Lawrence, Kansas, in 2016, and Mehrer charged him with habitual driving with a suspended license (and then let him drive away). The Kansas Supreme Court, however, said the officer had not done enough to justify the stop.
All that is needed for a traffic stop, the U.S. Supreme Court has ruled, is reasonable suspicion that the law is being broken, which can be a low hurdle. But the Kansas Supreme Court said Mehrer didn't even have that: He had only an "assumption" that the driver behind the wheel must be Glover.
"The problem is not that the state necessarily needs significantly more evidence; it needs some more evidence," the state court ruled.
Some justices, particularly Sonia Sotomayor and Elena Kagan, seemed to agree with their Kansas counterparts about the Constitution's protection against unreasonable searches and seizures.
Why should the court second-guess the trial judge, who said that in his experience many people lawfully drive vehicles not registered to them, Sotomayor asked.
Kagan hypothesized about a municipality that required motorists to carry their licenses with them at all times, but a survey showed that 50 percent of teenagers did so. "So now it's like common sense that if you see a teenager, she won't be carrying her driver's license with her," Kagan said. "Does that give the police officer the ability to stop every teenager that he sees?"
Justice Ruth Bader Ginsburg wondered whether it might be more likely that the person behind the wheel was not the registered owner with the suspended license.
Justice Neil Gorsuch said he was troubled that Mehrer did not testify, so there was no questioning about whether his experience or training caused him to "assume" that the driver was Glover.
"There are no facts in the record at all, zero," Gorsuch said. On the other hand, if all an officer had to do was say some "magic words" about his experience or training, "what are we fighting about here?" he asked.
At one point, Gorsuch seemed to adopt the accent of a street-wise New York cop, and Harrington drew laughter when she said, "This is Kansas, not New York."
"Touche," Gorsuch replied.
Justice Stephen Breyer said he believed it was at least reasonable for an officer to suspect the registered driver was behind the wheel, even if his driver's license was suspended.
Chief Justice John Roberts and Justice Samuel Alito seemed firmly on Kansas's side.
"Reasonable suspicion does not have to be based on statistics, it does not have to be based on specialized experience," Roberts said. "As we've said often, it can be based on common sense."
Harrington responded: "But, if they're just relying on an assertion of common sense, they have to give us some way to assess whether that is a reasonable common-sense inference."
Roberts said that was not the case. "I was just going to say if they're relying on common sense, they don't have to give you anything more than common sense."
Alito said that what Harrington was proposing - a look at the total circumstances surrounding an officer's decision to stop a vehicle whose owner has a suspended license - would make for "either a trivial decision or a revolutionary decision."
It's trivial if all that was lacking in Glover's case was a statement from the officer about his training, Alito said.
"It's a revolutionary decision if in every case involving reasonable suspicion there has to be a statistical showing or an examination of all the things that you think are necessary here."
The case is Kansas v. Glover.
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