The growing number of stealthy terrorists roaming the planet are keeping Nicholas Rasmussen, Director of the National Counterterrorism Center, up at night. In part one of an exclusive interview, he says the agency is stretched more “thinly now than they were five or six years ago.” He says it’s impossible to keep up with every terrorist and outlines the main challenge that ISIL poses in the aftermath of major terror attacks in Europe and the U.S.