I'm pretty sure the FBI should have been involved, seeing as how the kid was an obvious threat. Not just to Trump, but all the people at the rally, and probably other elected officials as well. He did have a vehicle with explosives in it, so he was probably planning a mass casualty event. But when he got there, and saw the utter lack of security for Trump, he decided to take out Trump first. He probably didn't count on the CS team taking him out so quickly, or at all, given the apparent amateur security measures taken at the event to protect Trump.
Caption this Meme