ABC News contributors Robert Boyce and Javed Ali break down how intelligence agencies work to stop sleeper cell threats. ––– Subscribe to ABC News on YouTube: https://abcnews.visitlink.me/59aJ1G Watch 24/7 coverage of breaking news and live events on ABC News Live: https://www.youtube.com/watch?v=gN0PZCe-kwQ&ab_channel=ABCNews Watch full episodes of World News Tonight with David Muir here: https://youtube.com/playlist?list=PLQOa26lW-uI8ixlVw1NWu_l4Eh8iZW_qN&feature=shared Read ABC News reports