Just after the strained relations between the U.S. and Turkey this summer finally began to heal, it seems a new crisis will emerge to test the NATO allies’ relationship. Turkey has long expressed its concerns about the U.S.’ partnership with the SDF, and YPG in particular, in Syria. This partnership has been essential to the U.S. goal of eradicating ISIS from Syria but is a national security concern for Turkey. The U.S. and Turkey’s roadmap deal for Manbij appeared to go a long way toward resolving the divergent issues, however, the U.S. is not following through with its side of the deal at an acceptable pace for Turkey. Expressing its disappointment with U.S.-backed YPG fighters not yet leaving Manbij, Turkey announced its intention to launch a military operation to remove all Kurdish forces from east of the Euphrates river in Syria. It should be noted that Turkey has previously launched operations to clear YPG fighters from west of the Euphrates, but has so far tried to find common ground with the U.S. On December 12, Turkish President Erdogan declared that “[Turkey] will begin our operation to free the east of the Euphrates from the separatist organization within a few days.” He noted the “target is not the American soldiers – it is the terror organizations that are active in the region.” This statement was met with a warning by the U.S., as a spokesman for the Department of Defense stated "unilateral military action into northeast Syria by any party, particularly as US personnel may be present or in the vicinity, is of grave concern. We would find any such actions unacceptable." The Pentagon stated the U.S. remains committed to Turkey’s border security and asserted that the SDF forces are a “committed partner against [Islamic State].”Following these statements by the U.S., Turkey’s Minister of the Interior asserted that Turkey would not be confined by the U.S. and would continue with its intended offensive. While there has yet to be a confirmation that Turkey’s military offensive has begun, there has been every sign that President Erdogan was serious about his declaration and intends to follow through with his plan. He reiterated his intent on December 17, stating that preparations for the operation are complete and that Turkey “can start our operation any moment now in Syrian territory.” He stated this can be done “without harming U.S. soldiers." On the same day, U.S. Special Representative for Syria Engagement James Jeffrey discussed the future of the U.S. partnership with the SDF, clarifying that the U.S. does not have “permanent relationships with sub-state entities” and views its current relationship with the PYD as tactical, transactional, and necessary to ensure the lasting defeat of ISIS. He specified that “the eventual goal with the SDF is for the SDF, just like the other political parties that we have supported in the past…to become part of the fabric of a changed Syrian society.” He also reaffirmed that the U.S. is “committed to Turkish security.” The Pentagon further communicated that the situation remains “fluid” and that the U.S. is in full coordination with Turkey. Given these recent comments, the question of how the U.S. will react to an attack on its local partners is at the forefront of everyone’s mind. Will Turkey’s proposed military offensive lead to a renewal of strain on bilateral relations? Or will the U.S. use this as an opportunity to begin disengaging from its Syria partners and Syria in general? Given reports of U.S. President Trump’s positive response toward Erdogan’s plans, the latter result seems most likely, although there has been a decided disconnect between Trump’s words and the Department of Defense’s actions in the past. Both Turkey and the U.S. have expressed their desire to work together in Syria, and Turkey is urging the U.S. to not allow “deep” disagreements over Syria policy to hinder future cooperation efforts. While Turkey’s offensive is not an ideal situation for the U.S., it does need to acknowledge that Turkey has a very real security concern that cannot be resolved solely by assurances. The U.S. will not be able to remain in partnerships with both Turkey and the SDF for much longer. Soon it will need to choose.