Last month the U.S., along with five Arab countries ,launched airstrikes on the Islamic State (ISIS) in Syria. The U.S.strikes also targeted the Khorasan group, a subset of al-Qaida that U.S. officials claim was plotting attacks on the West.

More broadly, Jabhat al-Nusra, the al-Qaida affiliate in Syria, also came under attack. Its fighters were also killed in the strikes, prompting calls from the leader of Nusra to retaliate against the U.S. and its allies.

There has been growing backlash in Syria against the U.S.-led campaign, particularly as reports of civilian death tolls emerge. Among the chief complaints is that the airstrikes have not targeted the government of Syrian President Bashar al-Assad. For Syrian rebels and opposition supporters, this created the impression that the Assad government is a de facto partner in the U.S. alliance, which the Assad government has encouraged by saying they had been briefed in advance about the strikes.

Here, Aron Lund, editor of Syria in Crisis at the Carnegie Endowment for International Peace, weighs in on the fallout and potential consequences of striking Jabhat al-Nusra.

Syria Deeply: The U.S. airstrikes in Syria targeted the Khorosan group, claiming that they posed immediate threats to U.S. National Security. What do you make of the Khorasan threat?

Lund: The Khorasan group is a term the United States decided to use for a specific network within al-Qaida. Media sources reported a few weeks before the strikes that U.S. intelligence sources said that there was a group led by Muhsin al-Fadhli, who may or may not be dead now, that started working with the Syrian al-Qaida affiliate Jabhat al-Nusra to start up a special operation to conduct strikes against the West.

Syria Deeply: Have these strikes managed to stifle their operations?

Lund: They hit a number of Jabhat al-Nusra camps in northwestern Syria, in Aleppo and Idlib. At the same time, the broader coalition hit the Islamic State further east and northeast. Jabhat al-Nusra members died in the attacks and in response some of their leaders issued martyrdom notices about some of their members. It’s unknown if Muhsin al-Fadhli died or not. There was also an interesting report from McClatchy that said one of the targets of the strikes was a defected French agent who had gone over to al-Qaida in Afghanistan and Syria.

Syria Deeply: Some of Syria’s rebels opposed the targeting of Jabhat al-Nusra on the basis that they are fighting both ISIS and the regime. Now some Syrians are rallying around them both, protesting against the U.S. strikes. What do you see as the fallout and potential consequences?

Lund: Many of the rebel groups have protested for a number of reasons. One is that they are basically disappointed that these strikes targeted a group fighting Assad instead of Assad himself.

Another element is that Nusra, unlike the Islamic State, is working among the other factions in Idlib and other villages were rebels are present, and some of them have good relationships with other rebel groups. They are fighting on the same front, working together to guard the same checkpoints, especially on the Islamic side of the spectrum.

It has even become a problem in the instances where they have strained relations with other factions such as U.S. and Saudi-backed factions. Jabhat al- Nusra is now aware that it is being informed on by someone on the ground, and that the U.S. and Saudi Arabia are training rebels to take them on. As a result, its possible you’ll see accelerating tension, and Jabhat al-Nusra going preemptively after these groups.

Syria Deeply: Are we seeing ISIS and Jabhat al-Nusra come together, under a common threat?

Lund: There have been a lot of rumors about that. There was an initiative by a number of Salafi- Jihadi clerics, some of which are very prominent and most of which are linked but not part of al-Qaida and Jabhat al-Nusra ideologically, who are looking for a ceasefire among jihadi rebel groups, to confront the common threat. For example, Abu Muhammad al-Maqdisi, a huge ideological figure in modern Jihadism who was just released from prison in Jordan, wanted a ceasefire between the jihadi groups.

They are obviously facing the same enemy: the U.S. and the U.S.-backed rebels, but at the same time, ideologically, on the top level, these groups have entrenched hostilities. The leader of The Islamic State has called himself a caliph, the leader of all the world’s Muslims, and there is little room for compromise there. Additionally, at the top level of these groups, there hasn’t been anything that indicates they really want a ceasefire. There could be a shift in priorities, but if there are ceasefires taking place right now, it is happening behind closed doors.

Syria Deeply: Jabhat al-Nusra has threatened revenge attacks in retaliation for coalition airstrikes. How seriously should those threats be taken? How capable are they of following through?

Lund: If you push them into a corner where they feel they are at risk of elimination at the hands of other rebel groups, why wouldn’t they fight back? They’ve had clashes before with U.S. and Saudi-backed rebel groups: they took over villages from peripheral factions of Jamal Maarouf’s Syria Revolutionaries Front in Idlib, so there is a conflict there.

In northwestern Syria, for a couple months now, there have been a long string of assassinations of rebel leaders, bombs against their headquarters, which anyone could be behind. The Islamic State is obviously trying to kill rival rebel leaders. The Assad regime also has an obvious incentive to blow up rebel leaders. Jabhat al-Nusra could potentially be behind these type of attacks if they are in a situation where they are weakened, under threat of airstrikes, and their rivals are getting more support from the U.S. and Saudi, but there is no real evidence of their involvement, that I know of that I know of that suggests this is happening right now.

Syria Deeply: The U.S. strategy relies on partnering with moderate Syrian rebel groups on the ground, as a kind of substitute for a Western-led ground invasion. Are there enough moderate fighters left, with the right capacity to carry out those plans?

Lund: The question for U.S. policy has always been how to define moderate. In a war like the one in Syria you can’t expect to find a certain quantity of rebels that match your criteria. Many rebels in Syria are probably for “rent”: they will fight for whoever will pay, give them weapons, security, protect their families – simply because the war has gotten so far.

For example, that is what the Saudis are doing; the Syrian Revolutionary Front wouldn’t exist if it weren’t for foreign funding. They give money, support, weapons, political support and leverage it in different ways. You have all of these different factions – from 5 to 500 people – who come together and say they are part of the Syrian Revolutionary Front because they benefit from it in some way.

The question for the U.S. has always been how much money and weapons they are prepared to throw into the war. If they want to back the rebels they have to be realistic and accept a certain level of risk, certain amount of weapons being lost, and defections to al-Qaida. If you want groups that are responsive to U.S. interests, the U.S. has to invest to create and build them; they won’t just find them.

If they don’t want to back the rebels, you have to assume that some of them will go to the Islamist groups because they have no other choice.

There is an interesting situation unfolding in Idlib and western Aleppo, which has always been the heartland of the rebel movement in Syria. Jabhat al-Nusra is being bombed by the U.S., new militias are being created, the Ahrar al-Sham leadership was wiped out in a bombing on September 9. There is a lot of movement there. Throw U.S. bombs into an already boiling kettle and there is no telling how it will play out.