Three minutes after the 911 call came in late Wednesday night, Sgt. Ron Helus of the Ventura County Sheriff’s Office pulled up at the Borderline Bar and Grill in Thousand Oaks, California, where a former Marine had burst in and began shooting patrons. Helus, a 29-year veteran on the overnight shift, met up with a pair of California Highway Patrol officers who had raced to the scene from a traffic stop, authorities said. They could hear gunshots. There was no time to wait for backup. “What you saw last night with the sergeant and California Highway Patrol officer, that is...