In this article, Daniel Byman demonstrates the assertion that American counterterrorism has settled into a “good enough doctrine,” meant to “manage, rather than eliminate, the terrorist threat”—with a degree of effectiveness that few imagined possible in the aftermath of 9/11.

In the 20 years since the 9/11 attack, U.S. counterterrorism policy has achieved some striking successes and suffered some horrific failures. On the positive side, jihadi organizations such as al Qaeda and the Islamic State (also known as ISIS) are now shadows of their former selves, and the United States has avoided another catastrophic, 9/11-scale attack. The worst fears, or even the more modest ones, of U.S. counterterrorism officials have not been realized. With terrorism less of an immediate concern, U.S. President Joe Biden has turned Washington’s focus toward China, climate change, and other issues—even withdrawing U.S. troops from Afghanistan as part of an effort to end the so-called forever wars.

At the same time, however, many of the United States’ more ambitious foreign policy efforts done in the name of counterterrorism since 9/11, such as effecting regime change in the Middle East and winning the goodwill of Muslims around the world, have failed and even backfired. Although al Qaeda and ISIS are far weaker than they were at their peak, they have persisted in the face of tremendous pressure, and their reach, albeit at times more ambitious than their grasp, has only grown since 2001. Today, other countries face potent terrorist threats, and al Qaeda, ISIS, and their various affiliates and allies remain active in civil wars around the world.