President Barack Obama’s announcement on Wednesday to strike the Islamic State militant group in Syria overlooked the other side of Syria’s double-barreled threat: President Bashar Assad. In taking out the Islamic State, experts say, Obama’s U.S.-led coalition might help Assad make territorial gains.

“One of the many things the president didn’t answer is if we attack ISIS (Islamic State) what are we going to do with Assad,” said Kori Schake, a research fellow at the Hoover Institution. Destroying the Islamic State “will make it easier for Assad to retake ground in Syria. The president needs to have a two-front war in Syria that destroys ISIL (Islamic State) and creates an alternate government,” Schake said.

Obama’s strategy to combat the Islamic State in Syria, also known as ISIS or ISIL, is two-pronged: arm the moderate rebels who are facing attacks from both the Assad regime and the Sunni militant group, and conduct an aerial campaign. And, while Obama called on Congress to approve further funding to train and arm the rebels, he emphasized the point that his strategy was in no way intended to help the Assad regime.

"In the fight against ISIL (ISIS), we cannot rely on an Assad regime that terrorizes its people; a regime that will never regain the legitimacy it has lost," Obama said, in his address Wednesday. "We must strengthen the opposition as the best counterweight to extremists like ISIL, while pursuing the political solution necessary to solve Syria’s crisis once and for all."

ISIS has been in Syria since the start of the civil war. Yet, over the past year, it has seized large portions of the country where it has set up a de facto hub of its self-declared Caliphate. Much of this land was seized from the same moderate rebel groups that Obama wants to support.

In July 2013, ISIS took control of the Al-Bab training camp, just north of Aleppo, and has seized virtually most of the al-Raqqa region in eastern Syria. These losses are just one reason why experts believe Syria’s moderate rebel groups are not the best allies in the fight against ISIS.

“Moderate rebel groups are ill-equipped and untrustworthy. Some of them, if not most, have links to extremist groups,” said Max Abrahms, a Northeastern University professor who focuses on terrorist organizations.

Certain rebel groups have pledged allegiance to ISIS, but not all of them, making the relationship between factions on the ground in Syria even more complicated. From a U.S. standpoint, at the beginning of the Syrian civil war, ISIS was lumped in the “rebel” side -- groups seeking to oust Assad. Later, moderate groups began clashing with extremist rebel groups, and when al-Qaeda’s affiliate in Syria, Jabhat al-Nusra, disowned ISIS, the militant group was left with very few allies.

The Assad regime then saw a small window of opportunity. ISIS, using its brutal tactics, was fighting the same rebel factions threatening Assad's forces. Assad and ISIS then began a kind of passive cooperation, turning a blind eye to each other's advances.

“Initially Assad kind of nourished ISIS,” Abrahms said.

However, the Assad regime is by no means an ISIS ally. Although the regime was “able to ignore ISIS in the short term, eventually they’re going to have to fight them,” Jacob Stokes, a research analyst at the Center for New American Security, recently told International Business Times. In the last month, Assad's forces have been heavily clashing with ISIS militants.

During the war, which has killed nearly 200,000 people, Obama had resisted direct engagement partially for fear of strengthening the Assad regime and partially because Syria lacks U.S. allies on the ground, experts said.

“Had Assad not used chemical weapons against his own people, the U.S. would already be bombing ISIS in Syria,” Abrahms said, referring to the chemical attack carried out by Assad forces last year that killed a thousand people. “The reason why we haven’t is because we don’t want to serve the interest of the Assad regime.”

Whether or not Assad's forces will be able to reclaim ISIS territory, if the U.S.-led coalition does succeed in defeating the militants, is still uncertain. But, one thing is clear, the U.S. and the Assad regime share a common enemy in ISIS.