The Syrian regime, with Russia’s help, is about to encircle and besiege hundreds of thousands of civilians in Aleppo, Syria’s second largest city. This will be a turning point for American national security, and not for the better.

The siege of Aleppo, unless somehow averted, will transform the Syrian opposition into something far worse for American interests at home and abroad.

The opposition forces now inside the city include U.S.-supported groups that are relatively independent from jihadist forces. They cannot prevent the encirclement of Aleppo, however, and may not survive the siege.

Those who do survive are more likely over time to submit to the leadership of Al Qaeda’s Syrian affiliate, Jabhat al Nusra, and other hardline elements that can help them endure when no one else offers assistance.  They may actually merge with these jihadi groups.

If America continues its inaction as the Russians and the regime tighten the noose around Aleppo, we may lose our best hope of forming a non-jihadi opposition we can work with.

Inaction and self-defeating diplomacy remain American’s policy, however.  We are begging the Russians to agree to a ceasefire without recognizing Russia’s true aims.

Russian President Vladimir Putin has deliberately created the policy crisis America now faces. He is not fighting ISIS and does not prioritize defeating jihadist groups in Syria.

Instead, Russian airstrikes are weakening the opposition’s defenses in the outskirts of Aleppo, setting conditions for a final assault by pro-regime forces. They are also destroying critical infrastructure and hospitals to force civilians to flee.

Assad has already reduced much of Aleppo to rubble using barrel bombs and airstrikes, and the humanitarian situation is dire even before the siege has begun.

Russia’s offer of a “cessation of hostilities” is duplicitous because it excludes Aleppo.  Any “truce” Secretary Kerry might obtain from Putin will only tie the hands of the international community while Russia helps Assad destroy the opposition.

The outcome of Russia’s intervention thus far has been better than Putin likely imagined. He is building an air and naval base on the Mediterranean, securing the Assad regime, and undermining NATO by provoking Turkey.

He is doing all of this unchallenged, and with a relatively minor commitment of resources. He has every reason to continue his current course.

The destruction of the non-jihadi opposition in Aleppo will be a strategic disaster. American national security depends on the destruction of ISIS and Al Qaeda, and opposition groups in Aleppo are among the strongest anti-ISIS actors in Syria. They have been fighting ISIS since early 2014 and want to destroy ISIS with American support.

But they will not abandon their war against Assad to fight ISIS, which the U.S. in the past has asked them to do in order to receive support. This is why U.S. programs have failed in the past. The U.S. would need instead to help these fighters against Assad and ISIS simultaneously in order to leverage them in the anti-ISIS fight.

Faced with imminent destruction at Assad’s hands, the threat of ISIS, and no help from the U.S., these groups will look to Jabhat al Nusra in desperation.

Jabhat al Nusra is already strong in northern Syria, where it is building a base for global jihad. It has nearly succeeded in completing such a base in Idlib Province. The U.S. cannot allow it to succeed in Aleppo, too, where opposition groups are still willing to constrain it.

The U.S. must act now to prevent Russia from producing an even more dangerous future for American security and to salvage what we can in the wars against ISIS and Al Qaeda.

The Obama administration should take three immediate steps put an obstacle in his path and preserve American options in Syria: provide immediate support to opposition groups in Aleppo; airdrop humanitarian supplies; and establish a safe zone along the Syrian – Turkish border.

Doing so will not stop Putin entirely, nor will it defeat jihadists that threaten the homeland.

But it will at least keep alive the option for the next U.S. president to recognize what America’s vital national security interests in Syria really are and act on that recognition. 

Jennifer Cafarella is the Evans Hanson Fellow and a Syria Analyst at the Institute for the Study of War. She is the co-author of "Jabhat alNusra and ISIS:  Sources of Strength" (February 2016) and "Syrian Armed Opposition Forces in Aleppo" (February 2016), as well as the author of “Jabhat al-Nusra in Syria: An Islamic Emirate for al-Qaeda” (December 2014).