Since 9/11, Washington has considered al Qaeda the greatest threat to the United States, one that must be eliminated regardless of cost or time. After Washington killed Osama bin Laden in 2011, it made Ayman al-Zawahiri, al Qaeda’s new leader, its next number one target. But the instability in the Middle East following the Arab revolutions and the meteoric rise of the Islamic State of Iraq and al-Sham (ISIS) require that Washington rethink its policy toward al Qaeda, particularly its targeting of Zawahiri. Destabilizing al Qaeda at this time may in fact work against U.S. efforts to defeat ISIS.

There is no doubt that relentless U.S. strikes in Afghanistan and Pakistan weakened al Qaeda by taking out the group’s central command and making it extremely difficult for it to plot attacks in the West. Pulverizing al Qaeda central also exacerbated difficulties it was already having in communicating with and supervising its various outposts. As a result, these branches either diverged from the parent organization’s strategy by fighting local regimes or overreached by targeting Muslim civilians, particularly Shiites. For example, Abu Musab al-Zarqawi, formerly the leader of al Qaeda in Iraq, carried out an unapproved attack in November 2005 that killed numerous civilians in Amman, which was also outside his area of responsibility. These distractions prevented the various branches from contributing much to al Qaeda’s overarching goal of fighting the West, or the “far enemy.” With the exception of its Yemeni subsidiary, al Qaeda’s franchises were largely limited to targeting the “near enemy” in their designated zones. And so, notwithstanding their contribution to the spread of al-Qaeda, its franchises were more of a liability than an asset to the brand name.

But today, al Qaeda, although still a grave threat, is only one of several emanating from the Middle East. Washington must not only contain Iran’s hegemonic aspirations, which threaten U.S. allies, but also fight ISIS’ expansion. Washington’s failure to balance these diverging interests became apparent when it made the mistake of coupling the bombing of ISIS targets in Syria with attacks on al Qaeda’s Khorasan group—operational cells affiliated with Jabhat al-Nusra (al Qaeda in Syria) that are planning attacks in the West. The double assault reinforced the jihadist narrative that Washington is hostile to Sunni Muslims and ready to bargain with the murderous Alawite regime of Syrian President Bashar al-Assad. Not only did the strikes give al-Nusra a boost in popularity—the Sunnis saw how a group focused primarily on fighting Assad was attacked by the United States—they also made it harder for Washington to persuade Sunni rebels to fight the Islamic State and prompted al-Nusra to attack U.S.-backed rebel factions in northern Syria. Earlier this month, Harakat Hazm, one of the main moderate rebel groups in Syria supported by the United States, announced it was disbanding after suffering defeats from al-Nusra.

Washington’s reluctance to deploy combat forces against ISIS has limited its options to airpower and a reliance on allies’ ground forces. There are some merits to this strategy and signs that it is indeed bearing fruit: ISIS’ astounding advance has been rolled back in some locations, such as in Sinjar, Iraq, and Kobani, Syria. But the unwillingness to invest greater American resources comes with a price: the United States is settling for limited and gradual progress, which is not enough to destroy ISIS.

Consequently, ISIS has adjusted to the U.S. air campaign by expanding beyond the Iraqi and Syrian theaters. It recently announced the creation of new wilayat (governorates) in Afghanistan, Algeria, Libya, Saudi Arabia, and Yemen and introduced a new slogan: “Remaining and Expanding.” A series of attacks by its agents in the Sinai Peninsula and in Libya gave credibility to its drive to grow and helped soften the blows from air strikes in Iraq and Syria.

In order for U.S. President Barack Obama to fulfill his promise to “degrade and ultimately destroy” ISIS, he must weaken ISIS’ control of Mosul, Raqqa, and other large population centers, as well as stop its expansion. Inadvertently, the administration’s cautious approach to military intervention makes al Qaeda—which views ISIS as a renegade offshoot—an important player in curtailing ISIS’ growth.

This advantage may not last long. ISIS’ surprising territorial gains and its ability to recruit an estimated 20,000 fighters (more than any terrorist organization since the 1980s, according to the International Centre for the Study of Radicalisation and Political Violence) are putting pressure on al Qaeda, particularly its various branches, to defect and jump on the ISIS bandwagon. By announcing himself as caliph, ISIS leader Abu Bakr al-Baghdadi has revealed that his ambitions extend beyond capturing Iraq and Syria. He has essentially demanded that all other jihadist groups pledge their allegiance to him. If Baghdadi were to succeed, he would command a much more powerful force, with assets throughout the Middle East, North Africa, and Europe. The pressure for all terrorist groups to unite under one camp only increased after the United States joined the fight against ISIS in August, when leading jihadists—such as Abdallah Muhammad al-Muhaysini in Syria, as well as Abu Qatada al-Filistini and Abu Muhammad al-Maqdisi in Jordan—called for all factions to overcome their differences and unify against American “aggression.”

Although al Qaeda agrees that jihadists should collaborate against their shared enemy the United States, it nevertheless refuses to join ISIS by following Baghdadi. Notwithstanding the fact that Zawahiri is less influential than his predecessor, he has so far been able to keep all of al Qaeda’s branches on his side. Although all the branches renewed their pledges to al Qaeda after Baghdadi announced his plans to create a caliphate, there was a leadership change in al Shabab (al Qaeda’s Somali branch), which made it more susceptible to defecting. However, Ahmed Umar, who in September 2014 succeeded Ahmed Godane, chose to renew his pledge to al Qaeda. As long as Zawahiri is alive, the leaders of al Qaeda’s branches who are beholden to him by personal oath are less likely to shift allegiances and join ISIS.

But if and when Washington succeeds in killing Zawahiri, the leaders of al Qaeda’s branches would have the opportunity to reassess whether to remain with al Qaeda or join Baghdadi’s caliphate. It is possible that Zawahiri’s successor will be able to hold al Qaeda together, particularly if it is Nasir al-Wuhayshi, al Qaeda’s so-called general manager and the head of its Yemeni branch. But it is more likely that in Zawahiri’s absence, al Qaeda would drift into ISIS’ camp, offering it manpower, resources, and access to arenas such as Algeria and Yemen where al Qaeda’s dominance has so far hindered ISIS’ expansion.

More so than during the bin Laden era, al Qaeda’s cohesiveness depends on the ability of its leadership to hold the various franchises together, and it is unclear whether al Qaeda can endure another succession since al Qaeda’s veteran leaders have dwindled considerably in recent years, making it more dependent on old guard figures such as Zawahiri to maintain unity. As such, the group’s fate may depend on Zawahiri’s personal survival. It is certainly ironic that at this point, when the United States is the closest it has ever been to destroying al Qaeda, its interests would be better served by keeping the terrorist organization afloat and Zawahiri alive.