On a shelf in his office at CIA headquarters, Director Bill Burns keeps a tiny scaled model of a house. It's the house in Kabul, Afghanistan, where Al Qaida leader Ayman al-Zawahiri was killed by a U.S. drone strike in 2022. When NPR went out to interview him last week, Burns pointed to the exact balcony on which Zawahiri was standing. There was pride in his voice. The CIA had never stopped looking for the guy even more than two decades after 9/11. But it was also a reminder of challenges, of adversaries that will outlast any single CIA director.Now, as Burns wraps up four years running the Central Intelligence Agency, the challenges have multiplied and intensified.For sponsor-free episodes of Consider This, sign up for Consider This+ via Apple Podcasts or at plus.npr.orgEmail us at [email protected](Image credit: Dee Dwyer for NPR)