In Yemen, the number of militants on the list has ranged from 10 to 15, officials said, and is not likely to slip into the single digits anytime soon, even though there have been 36 U.S. airstrikes this year.
The number of targets on the lists isn’t fixed, officials said, but fluctuates based on adjustments to criteria. Officials defended the arrangement even while acknowledging an erosion in the caliber of operatives placed in the drones’ cross hairs.
“Is the person currently Number 4 as good as the Number 4 seven years ago? Probably not,” said a former senior U.S. counterterrorism official involved in the process until earlier this year. “But it doesn’t mean he’s not dangerous.”
In focusing on bureaucratic refinements, the administration has largely avoided confronting more fundamental questions about the lists. Internal doubts about the effectiveness of the drone campaign are almost nonexistent. So are apparent alternatives.
“When you rely on a particular tactic, it starts to become the core of your strategy — you see the puff of smoke, and he’s gone,” said Paul Pillar, a former deputy director of the CIA’s counterterrorism center. “When we institutionalize certain things, including targeted killing, it does cross a threshold that makes it harder to cross back.”
For a decade, the dimensions of the drone campaign have been driven by short-term objectives: the degradation of al-Qaeda and the prevention of a follow-on, large-scale attack on American soil.
Side effects are more difficult to measure — including the extent to which strikes breed more enemies of the United States — but could be more consequential if the campaign continues for 10 more years.
“We are looking at something that is potentially indefinite,” Pillar said. “We have to pay particular attention, maybe more than we collectively have so far, to the longer-term pros and cons to the methods we use.”
Obama administration officials at times have sought to trigger debate over how long the nation might employ the kill lists. But officials said the discussions became dead ends.
In one instance, Mullen, the former Joint Chiefs chairman, returned from Pakistan and recounted a heated confrontation with his counterpart, Gen. Ashfaq Parvez Kayani.
Mullen told White House and counterterrorism officials that the Pakistani military chief had demanded an answer to a seemingly reasonable question: After hundreds of drone strikes, how could the United States possibly still be working its way through a “top 20” list?
The issue resurfaced after the U.S. raid that killed bin Laden. Seeking to repair a rift with Pakistan, Panetta, the CIA director, told Kayani and others that the United States had only a handful of targets left and would be able to wind down the drone campaign.
A senior aide to Panetta disputed this account, and said Panetta mentioned the shrinking target list during his trip to Islamabad but didn’t raise the prospect that drone strikes would end. Two former U.S. officials said the White House told Panetta to avoid even hinting at commitments the United States was not prepared to keep.
“We didn’t want to get into the business of limitless lists,” said a former senior U.S. counterterrorism official who spent years overseeing the lists. “There is this apparatus created to deal with counterterrorism. It’s still useful. The question is: When will it stop being useful? I don’t know.”
Karen DeYoung, Craig Whitlock and Julie Tate contributed to this report.