The United States and the West will need to rely on a combination of over-the-horizon counterterrorism options like the strike against Zawahiri, preserving some of the Afghan counterterrorism assets built up over the years and cultivating new ones, and counterterrorism defenses close to home.

The research reported here was funded in part by the Minerva Research Initiative (OUSD(R&E)) and the Army Research Office/Army Research Laboratory via grant #W911-NF-17-1-0569 to George Mason University. Any errors and opinions are not those of the Department of Defense and are attributable solely to the author.

Vanda Felbab-Brown is a senior fellow in the Strobe Talbott Center for Security, Strategy, and Technology in the Foreign Policy program at Brookings. She is the director of the Initiative on Nonstate Armed Actors.

Image: Reuters.