Twenty years after the deadly terrorist attacks of September 11, 2001, how has the global terrorist threat, and American strategy against it, evolved? And what lessons can we learn from the successes and failures of U.S. counterterrorism policy as we enter the third decade since 9/11? Two of the country's leading scholars of terrorist groups and counterterrorism assess twenty years of U.S. counterterrorism policy and the current state of the global terror threat. Matthew Levitt is the Fromer-Wexler Fellow at The Washington Institute and director of its Jeanette and Eli Reinhard Program on Counterterrorism and Intelligence. Aaron Y. Zelin is the Richard Borow Fellow at the Washington Institute for Near East Policy. Read Matt's presidential transition memo, Rethinking U.S. Efforts on Counterterrorism: Toward a Sustainable Plan Two Decades After 9/11: https://www.washingtoninstitute.org/policy-analysis/rethinking-us-efforts-counterterrorism-toward-sustainable-plan-two-decades-after Read Aaron's monograph, Your Sons Are at Your Service: Tunisia’s Missionaries of Jihad: https://www.washingtoninstitute.org/policy-analysis/your-sons-are-your-service-tunisias-missionaries-jihad; and his presidential transition memo, Syria at the Center of Power Competition and Counterterrorism: https://www.washingtoninstitute.org/policy-analysis/syria-center-power-competition-and-counterterrorism Middle East PolicyCast: Conversations on Middle East issues from the Washington Institute for Near East Policy.