operatestions in history go off without a hitch. catherine herridge live in washington with more on this. >> more than 28,000 security officials are protecting 100 square blocks from the capitol to where you are at the white house and beyond. 5,000 national guard troops on duty. 3,000 police officers. this is what is called a national special security event or nfsc, the highest security designation. that picture is different this year in two significant ways, that's the use of vehicles and drones as weapons. we recently sat down with the head of the secret service, who is in the lead. what concerns you most? >> everything concerns me. it's a constant battle of making sure that we've stayed in front of certainly the intelligence that we hear, but also any new emerging threats that may be out there. >> and then thale of the protes. that's sort of an overlay on this very dynamic threat environment. >> katdz rin, we understand there were -- catherine we