 This is All Things Considered from NPR News. I'm Elsa Chang in Culver City, California. And I'm Juana Summers in Washington. There is growing evidence of the seriousness of the security breakdown in Butler, Pennsylvania on Saturday, where former President Donald Trump was nearly assassinated. Multiple people on the scene have said they spotted the gunman on a roof outside the event and tried to alert police. NPR's law enforcement correspondent Martin Costi joins us to talk about the security implications of the Trump rally shooting. Hey, Martin.