The United States-led campaign against the Islamic State has yielded little tangible success so far. But things may suddenly have changed. The Telegraph reported Sunday that a Coalition bombing attack has killed a close aide to Abu Bakr al-Baghdadi, the Islamic State leader, near Mosul, Iraq. In addition, a member of the Iraqi parliament claimed that a separate attack near the city of al-Qaim injured al-Baghdadi himself, and that he is currently being treated in a hospital. The U.S. acknowledged that an attack on a convoy had taken place, but would not confirm that al-Baghdadi was among the dead of injured.

An injury or killing of al-Baghdadi would be a coup for the U.S., which has placed a $10 million bounty on his head. But previous experience with terrorist organizations has shown that groups tend to be resilient.

In 2006, a U.S. attack took out Abu Musab al-Zarqawi, a Jordanian militant who headed Al Qaeda's branch in Iraq. The moment was a clear victory for the Bush Administration, who had placed a bounty on Zarqawi's head. But the group survived and regrouped as ISIS. Al Qaeda itself, meanwhile, lacks the organizational strength it enjoyed under Osama bin Laden before his death in 2011. But the group has survived under his successor, Ayman al-Zawahri, and still has significant influence over its branches in Yemen and northern Africa.

The U.S.-led mission to degrade or destroy the Islamic State goes far beyond killing the group's top leadership. ISIS controls a large swath of land across Iraq and Syria, and has an estimated 30,000 fighters under centralized command—a number that has swelled through recruitment in foreign countries. ISIS earns significant revenue from oil sales and kidnapping and possesses large caches of weapons discarded or stolen from the Iraqi military. Neither the government in Baghdad nor the government in Damascus is powerful enough to rout them. And while the Obama Administration authorized 1,500 additional troops to expand the fight and train Iraqi forces, the president has ruled out use of American ground forces.

According to Aki Peritz, a former CIA counterterrorism official, al-Baghdadi's death would be welcome, but hardly a sufficient cause for victory.

"[It] will be cause for presidential speeches and commendations, but not the death of the Islamic State nor its loathsome ideology," he said.