The reported drone-strike death of the Pakistani Taliban leader (although Robert Gibbs cautions that it's still unconfirmed) is a tremendous short-term score for the U.S. The issue is whether this will be a substantive setback for the Taliban, or whether some new killer will simply take his place and continue business as usual. Peter Bergen examined this very issue in his great TNR piece a few months ago:

Daniel Byman, who runs the Security Studies program at Georgetown, has studied the effects that targeted assassinations have on terrorist groups. For years, the Israeli government has mounted assassinations against the leaders of groups like Hamas. Byman found that the dead leaders were replaced by more junior members of the group, "who are not as good; you drive down the age and experience of the leadership." A similar problem appears to be affecting Al Qaeda, according to Dennis Blair, the Director of National Intelligence. In February, he testified to Congress that "replacing the loss of key leaders, since 2008, in Pakistan's Federally Administered Tribal Areas has proved difficult for Al Qaeda."

 But I think Bergen would warn us not to get too cocky about Mehsud's death. He goes on to write:

[T]he drone program is a tactic, not a strategy. Bruce Hoffman, a professor at Georgetown widely regarded as the dean of terrorism studies, says, "We are deluding ourselves if we think in and of itself the drone program is going to be the answer," pointing out that the 2006 U.S. airstrike which killed the leader of Al Qaeda in Iraq, Abu Musab Al Zarqawi, did not exactly shut down the organization. Following Zarqawi's death, violence in Iraq actually accelerated.

Yes. Zarqawi was killed in June of 2006. It took more than a year after that, plus an American troop surge and the Sunni Awakening to before the insurgency subsided. As with Iraq, this was not the case of some unusually charismatic leader with a unique following. The slow and hard work of winning over the Pakistani and Afghan populations will have to go on long after Mehsud's name is forgotten.

--Michael Crowley