A Times investigation last year found that minor traffic stops in the United States were far more deadly than widely thought — in the previous five years, 400 unarmed motorists who were not under pursuit for any violent crime were killed by the police during such checks. We look at the different efforts across the country to rethink the stops and at the pushback from opponents who say that restrictions on the practice could keep more guns and criminals on the streets. Guest: David D. Kirkpatrick, an investigative reporter for The New York Times.