In a column a few weeks ago regarding the Insight Turkey Annual Conference, I gave a synopsis of the debate among the participants of a panel on Turkish-U.S. relations. Responding to a question on the panel about the possible "spoiler" of Turkish -US relations in 2016, there was a consensus among the panelists on the possible negative impact on bilateral ties by the Democratic Union Party's (PYD) armed People's Protection Units (YPG) in Syria. This issue has been negatively affecting the relationship between Turkey and Syria, especially over the last two years. Other than the immediate impact stemming from the publicity this disagreement involves, there is also the long-term problem that this tension is generating for mutual trust between the two countries. This is not the first time PKK-related issues have caused problems in bilateral relations. In the immediate aftermath of the U.S. invasion of Iraq, Ankara and Washington experienced tensions in bilateral relations because of the lack of satisfactory U.S. action against PKK targets. Increasing PKK activity and disagreement between Turkey and the U.S. during this period generated significant tension, while the difference between the two countries regarding the PYD and YPG started to create a more serious disagreement, deteriorating relations especially during the siege of Kobani. The fact that some U.S. officials publicly criticized Ankara for not doing enough in Kobani, and the fact that the U.S., despite opposition from Ankara, airdropped weapons to the YPG added to this crisis. For Ankara, the operational cooperation and membership overlap between the YPG and PKK make the two organizations one and the same. This overlap and cooperation could generate a major security risk for Turkey by increasing the capabilities of the PKK on the ground. There was already some concern within the Turkish security establishment about the PKK's unwillingness to pull its forces out of Turkey during the cease-fire period. The U.S. assistance to the YPG in this period both legitimized and emboldened the organization in the region. After the sudden termination of the cease-fire agreement, the PKK demonstrated that some of Turkey's concerns regarding the increasing sophistication of PKK operations were well-founded. Since then, the U.S. has stepped up its support for the YPG and Ankara has continued to express its concern meaning the discord between two countries continues to test their bilateral ties. In the meantime, Turkey faced a series of PKK attacks in southeastern cities and challenges to public order from its affiliated organizations. Since then, Turkey launched a major offensive against PKK targets. Operations against DAESH also intensified during this period. At this critical juncture, Ankara is facing two separate terrorist threats from two different organizations. While pursuing and intensifying the crackdown on these groups in Turkey, Ankara is also taking precautions to stop any form of infiltration by the members of these groups from Syria and Iraq into the country. On this point at least, there is not much difference of opinion between Turkey and US on how to fight DAESH with operational cooperation and coordination in border security arrangements between the two countries. Nevertheless, Ankara insists that the main problem is the state of affairs that Syrian President Bashar Assad's regime has generated and that a solution in Syria is necessary to resolve the widening regional crisis. What is more, the distinction that Washington claims to exist between the PKK and YPG is a problem to Turkish-U.S. relations. Washington seemed to recognize the concerns Ankara has conveyed about the YPG sufficiently enough to avoid them becoming a threat to Turkey, but there are serious concerns regarding operational cooperation, exchange of knowhow and membership overlap between the PKK and YPG. It will take stronger precautions to convince Ankara on the safety of American policy, and in the absence of such measures the issue will continue to be a spoiler for the two countries' relations. It can be expected that debates about the airfield in northern Syria will also be part of discussions in the coming weeks. [Daily Sabah, January 25, 2016]