Two months after Ankara threatened to launch an operation into northern Syria, where US forces are present, the US and Turkey seem to be working closely on a “security mechanism” that supposedly seeks to fulfill Turkey’s concerns about Syria.On Saturday, the sixth aerial overflight by the US and Turkey took place in eastern Syria. Under the “security mechanism” that was announced in August, the US and Turkey work together with military to military teams in Turkey that coordinate these flights and other issues in northern Syria. US Maj.-Gen. Eric T. Hill, commander of the anti-ISIS campaign, said these overflights were important for “all involved.”The problem for the US is that it has limited forces on the ground in eastern Syria, and is trying to simultaneously balance several challenges. First, it wants to continue the mission to defeat ISIS. This has been successful because of the partnership with the Syrian Democratic Forces, a group that includes Kurds and others in eastern Syria that the US has helped train, assist and advise during the war on ISIS. The SDF liberated Raqqa in 2017, and in the spring of 2019 ISIS was finally defeated in its last stronghold near the Euphrates River. But ISIS sleeper cells remain a threat.Second, the US faces a continuing problem in Al-Hol camp, where tens of thousands of ISIS supporters ended up after the defeat of ISIS. The camp’s residents are becoming increasingly radicalized as they use their ability to move freely within the camp to reorganize ISIS cells and support ISIS.Meanwhile, other ISIS male members held in detention in eastern Syria remain without trial because their home countries will not take them back, and the eastern Syrian authorities linked to the SDF have not found a way to constitute war crimes trials for the ISIS perpetrators. Hill called the issues in Al-Hol a “wicked problem,” according to a tweet by the Special Operations Joint Task Force.A third challenge for the US is placating Turkey, which continues to threaten to launch a military operation in eastern Syria. Despite the US overflights and getting the SDF to destroy defensive fortifications in areas in eastern Syria, Turkey President Recep Tayyip Erdogan said that his country could still act if a “safe zone” is not established in Syria. Turkey once again says its “preparations” for an offensive are complete, and that the US is moving to slowly to pave the way for Turkey’s safe zone that will extend 32 km. into Syria.Rather than respond to the constant threats and claims the US is aiding terrorists, the US seeks to work more closely with Turkey.Washington hopes that it can thread the needle of pleasing Turkey and the SDF by removing the SDF from the border without ending up with a Turkey military operation on its hands that would alienate the SDF partnership.In short, the US goal increasingly appears to be to get the SDF to keep fighting ISIS in one part of eastern Syria, while other parts of eastern Syria are quietly cleared of the SDF. But will that be enough for Ankara, or is it only phase one before Turkish troops move into northern Syria anyway? The SDF Twitter account says the SDF is committed to both defeating ISIS and the US-backed security mechanism. “The work continues to remove fortifications in the areas that concern Turkey.”There is no evidence Ankara is pleased. Instead, it likely thinks that more threats will get it a larger role in northern Syria, and it understands that eventually it will create daylight between the US and the SDF, damaging the SDF partnership and forcing the US to choose between Ankara and eastern Syria.For now, the SDF is vacillating in the hope of preventing a Turkish military operation. In January 2018, the SDF watched as Turkey took over Afrin and 160,000 Kurds were made homeless while Syrians from other parts of Syria were settled in Afrin, changing the demographics of the historically Kurdish area. The SDF knows that enabling, even by policy errors, another Afrin in eastern Syria would be seen as a monumental betrayal by locals who helped defeat ISIS.But the cards are stacked against the SDF. The Trump administration wanted to withdraw from Syria in December 2018. To buy time, commanders noted that ISIS wasn’t defeated. The only way the SDF can continue its role is to be seen as essential to defeating ISIS. It is essential. But can it be used to fight ISIS in one area and removed from other areas?The US European Command is pleased with the joint work by Turkey, seeing it as a way to reduce tensions between Turkey and the US. In a September 18 briefing, Chris Maier, director of the Defeat-ISIS Task Force, discussed the security mechanism.The US says it has made a bilateral agreement with Turkey, and established a joint operations center in southern Turkey. Through this, the US gets the SDF to remove fortifications while it conducts aerial flights and ground patrols with Turkey. The US says that it is now training more local security forces in eastern Syria, and working for the “safe, voluntary and dignified” return of refugees.Turkey has declared it wants to resettle in eastern Syria one million Syrian refugees now in Turkey. The US was asked at the September 18 meeting if Turkey will eventually control the “safe zone” it demands. The US said it was working on a military arrangement that ensures security. “As to the longer term implications for the security mechanism, we remain focused on protecting Turkey security concerns and taking those into account while at the same time maintaining the [Defeat] ISIS campaign.”The US says that its initial steps include an area along the border from Tell Abyad to Ras al-Ayn. The word “initial” indicates more is to follow. The US says it has talked with Turkey, and that “we have an understanding of where the initial steps will occur.” However, Washington refuses to provide numbers or guidance on how far the security mechanism will go.The September 18 news conference indicated the security mechanism could result in Turkish forces moving into northern Syria in areas from which the Kurdish People’s Protection forces have been removed. According to the statement, the US is setting up local forces but doesn’t want a security vacuum to result.“That may ultimately result in needing more forces that we would work with, with Turkey and others, to address,” the statement said.The US says it is “inserting US military and Turkish military into an area to execute patrols, aerial reconnaissance, and in some cases removal of fortifications.” The US also provides a monthly report to Turkey about supplies, including arms and vehicles, sent to eastern Syria. But the US says that it is convinced “as we work with Turkey, the idea of a Turkish incursion into Syria has gone down substantially.”Time will tell if the US-backed security mechanism is a way for Turkey to achieve a permanent military presence in northern Syria, or just a way to delay another crises with Ankara and keep US partners fighting ISIS. For now, it appears that the mission to defeat ISIS is increasingly focused on trying to manage a complex relationship with Turkey, and that the US is becoming more involved in the minutiae of who controls what at the level of the local councils.Given the US record at trying to manage state-building and these kinds of controversies elsewhere, it would be surprising if the security mechanism doesn’t merely put off deeper questions for the next few months until a new crisis emerges.There doesn’t seem to be any way to both satisfy Ankara’s view and continue to get the SDF to fight ISIS. In the long term, Ankara understands the more it pressures the US, the more the US will work with Ankara, and the more the SDF will come to realize it is fighting to keep Raqqa safe while being asked to hand over other parts of eastern Syria to another Afrin-style incident.Should the SDF provokes a crisis with the US, it will be seen as an unreliable partner, accused of working with Damascus and fueling Turkey’s claims for northern Syria. For ISIS sleeper cells, nothing could be more pleasing than to watch this policy chaos unfold two years after losing Raqqa.