The United States and its coalition partners have conducted close to 800 airstrikes against Islamic State targets in Iraq and Syria, hitting command-and-control facilities, training compounds, armored vehicles, oil refineries, supply trucks, artillery pieces, and bunkers. But there's a notable absence from the target list: the Islamic State's top leaders.
Since the Obama administration's bombing campaign began in Iraq on Aug. 8, the United States has not conducted what's called a "decapitation strike," an attack specifically aimed at taking out a member of the Islamic State's senior military commanders.
The tactic's absence from the military campaign is particularly glaring because hunting high-value militants has become a cornerstone of the Obama administration's counterterrorism strategy in other parts of the world.
In his Sept. 10 speech unveiling his campaign against the Islamic State, President Barack Obama said his plan to fight the militant group, which is also known as ISIL, would be similar to the approach used in Yemen and Somalia, where the United States has taken out "terrorists who threaten us, while supporting partners on the front lines."
But according to a U.S. defense official, none of the airstrikes conducted so far have been "intended to cut the head off the snake."
A September airstrike in Mosul reportedly took out a top aide to Abu Bakr al-Baghdadi, the Islamic State's leader, but the U.S. military has not confirmed the death of Abu Hajar al-Sufi. Hundreds of Islamic State fighters are believed to have been killed after months of U.S. bombing, but none of the group's other top leaders have reportedly died in an airstrike.
Still, while the United States has yet to target the group's leadership, military officials hint that such strikes are coming.
"Without talking about potential future operations, we've long said it is important to disrupt ISIL's ability to lead, command, and control its forces and, broadly speaking, I can assure you we will continue to conduct targeted airstrikes in Syria and Iraq against ISIL as necessary," said U.S. Central Command spokesman Maj. Curtis J. Kellogg.
The wait is partly due to resources. Going after high-value individuals is time-consuming and labor-intensive, and the demand for surveillance and reconnaissance drones is already high, especially while the United States still has so many troops still stationed in Afghanistan.
"As the campaign against ISIL matures, and the U.S. brings in more resources to support the Iraqis, there will be an increased focus on high-value individual targeting," the defense official told FP.
But the United States has to find the Islamic State's leaders before it can try to take them out, and this is also going to require more human intelligence from sources on the ground. The need for precise information is particularly vital because many potential militant targets work in or travel through major population centers like the northern Iraqi city of Mosul, which means that an errant strike could cause significant civilian casualties.
Thomas Sanderson, a senior fellow at the Center for Strategic and International Studies, said the United States is trying to build the networks of relationships needed to collect human intelligence in Iraq and Syria, but it's difficult work.
During the wars in Iraq and Afghanistan over the last decade, U.S. military officers were out in villages, overseeing civil works projects that created goodwill and building rapport with locals, who would then be more willing to share information, he said.
But the relationships built in Iraq over the last decade were not maintained when U.S. troops left in 2011. With their departure, U.S. spies largely left the country, too.
U.S. special operations forces and other intelligence officials are trying to build these contacts now, but on a much smaller scale and under very different circumstances. In Iraq, the U.S. military can rely somewhat on the intelligence sources of the Iraqi security forces, but in Syria there are even fewer reliable relationships.
One exception is in Kobani, the Syrian-Turkish border town where the United States is working with the Syrian Kurdish fighters there to identify Islamic State targets to bomb.
"The same thing is needed to hunt down Baghdadi," Sanderson said. "When you kill the leader, it demonstrates that anyone is vulnerable."
Since the airstrikes began, the Islamic State has predictably adapted its behavior, hiding fighters among local populations in towns and cities, scaling back its use of electronic communications, and no longer moving in the open in big formations.
"They have gone to ground inside cities and this makes decapitation strikes very difficult," said David E. Johnson, a military expert at the Rand Corp. "You can't kill them if you can't find them."
The Islamic State has both a large area in which to operate and access to cities where its leaders can hide among the population, which further complicates targeting them without killing civilians.
But even if the United States had all of the intelligence it needs, there are questions about the wisdom of this approach, said Colin Clarke, who focuses on counterterrorism and irregular warfare at Rand.
There is a long-standing debate over whether these kinds of strikes introduce more problems than they solve. For example, they create martyrs who are then used for recruitment purposes. Plus, civilians are often inadvertently killed and this drives up popular support for the targeted group.
Israel has assassinated several of Hamas's top commanders over the last decade, often through airstrikes that have sometimes also killed civilians, including children. The strikes have dealt significant blows to the group's leadership, but they have also bolstered public support for Hamas.
In addition to legal and moral questions, there is also the strategic problem of killing an established leader and having him be replaced by an unknown quantity.
"When you take out a leader, you run the risk of creating your own intelligence blind spot," Clarke said. "It's about the devil you know versus the devil you don't know."
Figuring out Baghdadi's role within the organization is likely a big focus of the intelligence hunt right now, Clarke said. Is he the lynchpin of the group? How does the network operate? Who are the real power brokers?
"Despite the vast amount of publicity and analysis [the Islamic State] has generated since 2011, verifiable facts concerning its leadership and structure remain few and far between," said a recent report from the Soufan Group, a security and intelligence company.
For the moment, Baghdadi holds a position of "unchallenged authority," the report says. "He has not needed to be a visionary or a natural leader, just strong enough to impose his will more effectively than anyone else."
His location is unknown, but he is believed to run the Islamic State from its stronghold in Raqqa, Syria, "though spending time also in Mosul," according to the Soufan Group.
His first public appearance was in July, when he led a prayer service at Mosul's Great Mosque, an audacious move for himself and the group.
His two deputies -- Abu Muslim al-Turkmani and Abu Ali al-Anbari -- were formerly members of the Iraqi Baath party. Turkmani is "reported to have been a senior Special Forces officer and a member of military intelligence," the Soufan Group's report says.
The effectiveness of a U.S. strike against Baghdadi would partly depend on how much power he delegates to these deputies and his other commanders. If Baghdadi's successor is clearly delineated, then removing him would have less of an impact.
Clarke said the lack of drone strikes against Islamic State leaders is most likely due to a lack of human intelligence and deliberation over what effects such strikes will have.
"Both things are confounding the administration right now," Clarke said.