 NPR's Don Gagne reporting. Wisconsin Senator Ron Johnson says the Secret Service was aware of a possible threat one hour before the attempted assassination of Trump last weekend. NPR's Luke Garrett reports. Senator Johnson, a senior member of the Senate Homeland Security Committee, received an unclassified briefing on Wednesday. During the discussion, a fellow senator asked when the Secret Service first learned of a possible threat at the rally. We found out it was more than 60 minutes before the shot.