America’s unique, enduring gun problem, explained

Three people were killed and another injured in a mass shooting at the University of Nevada, Las Vegas on Wednesday.

The shooter, a former college professor in his 60s who reportedly had applied for a job at the university, was killed in a shootout with police. Further details about his motive and the gun used in the attack were not immediately known.

The shooting was one of several hundred mass shootings this year, and it took place not far from the site of the deadliest mass shooting in modern US history, in...