Terrorists like to travel. Terrorist groups like ISIS and al-Qaeda depend on travel, said Ambassador-at-Large and Coordinator for Counterterrorism Nathan Sales to Trans-Atlantic alliance partners at a recent conference hosted by the German Marshall Fund. They have to travel to receive training. They have to travel to case their targets. They have to travel to carry out their attacks. Every time they board a plane or cross a border, we have an opportunity to detect and capture them.When ISIS attempted to create a physical Caliphate, an unprecedented number of foreign terrorist fighters – roughly 40,000 people – flocked to the war zone in Syria and Iraq. And now that we've liberated some 98 percent of the territory ISIS once held, there's a risk that some of these battle-hardened veterans will return home or relocate to third countries. To identify terrorists or suspicious persons hiding among international travelers, the United States uses PNR, or Passenger Name Records, to search out those who may pose a threat and should be prioritized for additional screening.