 Investigators are now trying to piece together how a gunman armed with an AR-style rifle was able to get in place to injure Trump at his rally in Pennsylvania. Former Secret Service Deputy Director A.T. Smith is a CBS News consultant. There is no explanation whatsoever for how an individual was able to get on top of a building and be that close with a long rifle. And the FBI's investigation, working hand-in-hand with the Secret Service, will look at every aspect of this.