Byline: Bruce Riedel

It's far from over. There's a rising power who's ready to adapt al Qaeda to the times.

Osama bin Laden's death is a major but not fatal blow to Al Qaeda. The terror group has powerful allies in Pakistan, now its key target, and remains deadly. It has evolved enormously since 9/11, and its decentralized infrastructure makes it less vulnerable. But it is behind the power curve in the Arab world, which is changing faster than Al Qaeda. Bin Laden's successors will need to adapt or risk becoming marginalized outside Pakistan and Yemen.

Ayman al-Zawahiri has taken an increasingly critical role. He, far more than his dead boss, has been Al Qaeda's public face in recent years, speaking out more often and even writing a book last year on how to overthrow Pakistan--a country struggling against jihadism like no other, and, as the world's fifth-largest nuclear power, a place that keeps the Obama national-security team up at night. Zawahiri was the target of the joint U.S.-Jordanian operation in December 2009 that ended when a Qaeda double agent blew up the CIA's base camp in Afghanistan, killing more spies than in any disaster since Beirut in 1983. …