Recruiting, building and cultivating the group, planning operations—all were tasks that for years fell to bin Laden. Since his death, experts say, it appeared al-Libi had taken on a larger role in each area.
"Al-Zawahiri doesn't have the tools to run this organization on his own," says Nelson. "Any strike like this one is a success. But it's not a cause for celebration. There's still a lot more work to do against al Qaeda."
John T. Bennett covers national security and foreign policy for U.S. News & World Report. You can contact him at email@example.com or follow him on Twitter.