( CNN ) -- Despite facing a punishing air bombing campaign , the Islamic State in Iraq and Syria continues to march across Syria . This week , it tightened its siege on the Syrian Kurdish town of Kobani . Though it is too soon to write off the American strategy to `` degrade and ultimately destroy '' ISIS by relying on air power and Syrian rebels , the opening week was a box office flop . For the operation to be a success , Washington should enlist the support of a group it has spurned : the Syrian Kurds . To explain : ISIS is the most powerful fighting force across northern and eastern Syria . Its main Islamist competitors have all been weakened in recent months . The Salafi brigade Ahrar al-Sham has seen its stock plummet after Qatar curtailed its funding and its leader died . ISIS chased the al Qaeda affiliate Jabhat al-Nusra out of its eastern strongholds of Deir al-Zour . And the Tawhid Brigade has been adrift ever since the death of its leader last year . But Washington is not pinning its hopes on these politically unsavory groups to dislodge ISIS . Instead , it has armed smaller and less powerful brigades from the loose umbrella organization known as the Free Syrian Army and has announced a program to train 5,000 rebels in Jordan and Saudi Arabia . Equipping the Free Syrian Army got off to a rocky start . Sources in Turkey told me this summer that one brigade tried selling American-supplied TOW anti-tank missiles to Jabhat al-Nusra for $ 25,000 this year . Throwing money , arms and training at Free Syrian Army units will not defeat ISIS . Instead , it will require a fundamental shift in the Free Syrian Army 's thinking . One of ISIS ' chief strengths is its unit cohesion . Its cadres are ideologically bound , fighting for the cause of Islam . These doctrinal bonds ensure that units stick together when they come under fire . In contrast , Free Syrian Army brigades often battle for material gain and social status . In combat , their forces frequently disintegrate , no longer acting as a team . I witnessed this myself while spending time with them on the front in 2012 and 2013 . There are also more mundane challenges . There are no rebel outfits that can confront ISIS in its Syrian bastion of Raqqa . In the summer of 2013 , the city 's strongest Free Syrian Army contingent , a loose alliance known as the 11th Brigade , mostly folded into Jabhat al-Nusra . When fighting erupted between ISIS and other organizations at the end of 2013 , ISIS ejected Ahrar al-Sham from the town . Today , it reigns supreme in Raqqa . To lay siege to the city , Free Syrian Army groups would have to travel approximately 100 miles from their northwestern strongholds in Aleppo and Idlib . Logistical constraints -- these brigades rarely fight beyond their home regions -- would make resupplying forward units with ammunition , food and fuel unfeasible . And if Washington is hoping for a civilian uprising to topple ISIS in Raqqa , it might have to wait until the Armageddon jihadists are predicting will occur in Syria . The Western media have depicted ISIS-controlled areas as slave markets where a terrorized civilian population lives in constant fear . But there 's evidence that many do not harbor such trepidation . Raqqans I spoke to via Skype and in Turkey said that many in the city support ISIS . And why would Syrians acquiesce to a group that seeks to control most facets of their lives ? Because , as President Bill Clinton famously quipped , `` It 's the economy , stupid . '' In a war-torn country where civilians wait in line for hours to get bread , where they endure constant power outages and are hard-pressed to obtain fuel , Raqqans live on a paradise island of commodities . ISIS ' oil fields provide gas , its dams deliver electricity , and its efficient bureaucracy ensures that groceries are stocked with sufficient supplies of basic staples . President Barack Obama may believe that ISIS `` is certainly not a state , '' but the Syrians under its control are grateful for its state services . Most important , the group ensures security in a country where there is none . The chaos and plunder that characterize Free Syrian Army-controlled areas are a distant nightmare . While the partially rebel-controlled city of Aleppo could be a stage set for a `` Mad Max '' sequel , ISIS ' Raqqa is a field of dreams . The only other rebel-held areas that have a modicum of order are those under the control of the Kurdish Democratic Union Party ( PYD ) . The group rules the northern city of Qamishli and the villages surrounding it . Unlike Aleppo , the economy has not collapsed , and residents do not cut down trees for warmth . And in contrast to Raqqa , the secular Kurds have not driven out Qamishli 's Christians but instead have protected them . Moreover , Turkish fears that a Kurdish enclave would provide a safe haven for Turkish Kurds from the Kurdistan Workers Party ( PKK ) have proved unfounded . The Democratic Union Party has ensured calm on the border , and a grateful Turkish government has reciprocated by meeting with its leaders . But the Kurdish Democratic Union Party 's greatest asset is its willingness to fight ISIS . Long before Free Syrian Army brigades were willing to take on the jihadists , the Kurdish Democratic Union Party made the battle against them its chief objective . And while Free Syrian Army groups receiving arms from Washington , such as the Hazm Brigade and the 13th Division , have condemned the American airstrikes , the Kurdish Democratic Union Party has welcomed them . Yet despite this alignment of interests , Washington has shunned the group . It refuses to recognize the Kurdish Democratic Union Party or support it , because of its ties to the Kurdistan Workers Party , a State Department-designated terrorist organization since 1997 . In a country where America has so few allies , a change in policy is warranted . Relying on insignificant Free Syrian Army units will not be enough to topple the ISIS behemoth . Working with the Kurdish Democratic Union Party could help Washington reach its objective of destroying the organization .
Barak Barfi : As airstrikes against ISIS fail , Washington should look to Syrian Kurds . ISIS is strongest force in northern , eastern Syria , he says ; Islamist rivals are weakened . He says Kurds eager to fight , can supply the kind of order ISIS brings to conquered cities . Barfi : Do n't rely on Free Syrian Army ; Kurds ' objectives more in line with D.C. 's .