For some time, it has been obvious that the United Nations' plan for Syria is a dead letter. As the regime of Bashar Al Assad has regained territory, all talk of transferring power away from the Syrian president, the cornerstone of the UN plan, has become pointless. However, Mr Al Assad's hold on power remains vulnerable while foreign forces remain on Syrian territory and the reconstruction of the country looms large.
Two foreign states opposed to Bashar Al Assad, the US and Turkey, can potentially have a major influence on what happens in Syria. For that to happen, however, both will need to move beyond their differences and co-ordinate their policies against Mr Al Assad. This is by no means guaranteed, as each side is pursuing very different objectives there.
Turkey has occupied a large portion of northern Syria through its Euphrates Shield and Olive Branch military operations, as well as its intervention in Idlib. Ankara also has control over several million Syrians, between the inhabitants of the areas it controls, refugees and internally displaced people. While the Turks have participated in the Astana negotiations, any disintegration of this process and a return to conflict would leave it with significant leverage in Syria.
The US, in turn, is present in north-eastern Syria, particularly in Al Hasakah Governorate, where the borders of Syria, Turkey and Iraq meet. Its influence stretches down to the middle of the Euphrates valley, with an outpost in Al Tanf in Syria’s south-east, on the road between Damascus and Baghdad. A number of those areas are where Syrian oil is produced, so as long as US forces remain there, they will deny Mr Al Assad a major revenue source.
Yet the obstacles that the US and Turkey face are far from negligible. To begin with, both sides have been opposed when it comes to Syrian Kurdish forces, which Ankara would like to neutralise militarily and keep away, as far as possible, from Kurds in Turkey. The US, in turn, views Kurdish forces as a key ally in preventing the return of ISIS to Syria and has not taken kindly to Turkish President Recep Tayyip Erdogan’s vow to deploy his army to the Iraqi border.
To ease tensions with Turkey, the Americans announced last week that they would be placing observation posts in northern Syria to help secure the Turkish border. The implication was that the US wants to ensure that the Kurds will not challenge Turkish red lines in the area. Yet it is equally true that by creating these positions, the Americans are also drawing a line against any Turkish incursion into those parts of Syria against the Kurds. They fear this might draw Kurdish forces away from the middle Euphrates valley where they are fighting ISIS.
Turkey also has to face an uncertain security situation in the areas it governs in Syria and is reluctant to take steps that might undermine its relations with Russia, with whom it is participating in the Astana process. That is one reason why the Russians have tiptoed around Turkey in Idlib, because they too want to avoid a break with Ankara, which could seriously damage their efforts to consolidate an emerging regional consensus around Mr Al Assad's rule.
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Yet where the US and Turkey can be effective is in jointly defining their aims in Syria and pushing more strongly for the departure of the Syrian leader. Russia would not be able to ignore US-Turkish actions on that front. That is why Russian President Vladimir Putin has been so keen to secure funding from European states for post-war reconstruction, hoping that if he can get such pledges, it would offset US and Turkish pressures against the regime.
In many ways, the tangled interests in Syria are a Mexican stand-off, with each side pointing a gun at the other. This will shape the possible outcomes. Turkey and the US might raise the heat for Mr Al Assad’s departure but all that might do is exacerbate the stalemate that perpetuates the refugee crisis. The Syrian regime, in turn, can take maximalist positions but that would only encourage Washington and Ankara to ensure that no funding goes to reconstruction, which will hurt Mr Al Assad.
That is why the US must consider entering the negotiations over Syria, in collaboration with Turkey and after having agreed common objectives with regard to the Assad regime. Only by doing so would the two sides be able to better affect the political outcome in Syria and engage with Russia over this while perhaps marginalising Iran. Now is the time to move talks over Syria to a stage where the major adversaries of Mr Al Assad can also negotiate an endgame.
That will not be easy and the Syrian regime, Russia and Iran have the latitude to make life difficult for the Turks and the Americans. However, it is equally true that in comparing strengths, the Americans and Turks are nearly as strong as the Syrian regime’s allies. Moreover, Russia will be cautious before ruining its careful plans to bolster Mr Al Assad. For the US and Turkey to make headway in Syria, they have to agree a common strategy that transcends their previous disagreements.
Michael Young is editor of Diwan, the blog of the Carnegie Middle East programme, in Beirut