Guy Bartkus exhibited warning signs prior to the attack that should have been reported to law enforcement, the city’s police chief told CNN Monday.

One person was found dead, and the FBI said it was sending investigators, including bomb technicians, to the scene.

Bruce Springsteen’s criticisms of Donald Trump last week appear to have triggered the president even further, as he is now calling for an investigation of the superstar singer’s endorsement of Kamala...