 Retired Tulsa Police Sergeant Dave Walker, who has 10 years of SWAT experience, reacts to the shooting. Dave Walker says training for events like rallies happened well before the event even takes place. He says Secret Service did exactly what they were trained to do, but their lives between Trump and any prudential danger. He says next they will look at how this could have been prevented. The investigation begins as to how we could have prevented it for the next one. It's not the first candidate. It's not the first president to be shot.