Hypothetically, American drone bombings in Pakistan are supposed to be killing off al-Qaeda's leadership. But in actuality, the strikes kill more people who aren't in the terrorist group's command structure.
Council on Foreign Relations fellow Micah Zenko dug up a 2011 assessment, from Pentagon official Michael Vickers, that there were "perhaps four important Qaeda leaders left in Pakistan, and 10 to 20 leaders over all in Pakistan, Yemen and Somalia." Zenko then compared that number to an average of several estimates of people killed in drone strikes:
Since Vickers' estimate that there were two dozen al-Qaeda leaders left in 2011, more than two-hundred U.S. drone strikes have killed upwards of 1,200 people — apparently non-al-Qaeda leaders.
Zenko's comparison makes a very clear point: unless Vickers's estimate in 2011 was a dramatic lowball, it's just wrong to say that the drone campaign is narrowly tailored to killing top al-Qaeda officials. It's killing many more people than that, including hundreds of civilians and, recently, an American and Italian hostage. And even if American drones campaign took out top al-Qaeda officials in the process, it's genuinely unclear how much that would damage the group.