The United States has resolved to pull its forces out of Syria. On Dec. 18, U.S. President Donald Trump reportedly made the decision despite arguments from the Department of Defense and the State Department that U.S. troops should remain in the country. Trump's choice appears final, but this is not the first time he's considered such a withdrawal. Earlier in 2018, Trump reportedly ordered the Pentagon to begin planning for an exit, but he was dissuaded by his advisers. Rather than prepare for a departure, the United States expanded its goals in Syria to include an indefinite stay and a renewed strategic focus on countering Iran's presence there.
The United States again appears headed for the exits, which would affect U.S. interests in several ways. On the positive side, a pullout would free up about 2,000 troops — mostly from elite units — for deployment elsewhere. Moreover, a departure would dramatically reduce the risk that the United States will find itself in a dangerous, unplanned clash with any of the many powers in Syria's crowded battle space. The greatest positive, however, would be a clearer path toward improved relations with Turkey, which is a critical partner in the U.S. security strategy for the Middle East and Europe. Ankara has been gunning for an opportunity to launch a direct operation against the People's Protection Units (YPG) — a Kurdish militia that has enjoyed U.S. support — but the U.S. presence has insulated the YPG from attacks by the Turkish and Syrian governments.
On the negative end of the spectrum, a U.S. departure and the likely Turkish assault on YPG positions thereafter would have a detrimental effect on the campaign against the Islamic State. The YPG forms the bulk of the Syrian Democratic Forces (SDF), which is at the forefront of the fight against the Islamic State in eastern Syria. The Islamic State has lost significant ground, but the group is far from defeated, and U.S. intelligence believes that about 15,000 fighters remain in Syria, as of August 2018. If the SDF becomes distracted by a U.S. withdrawal and a confrontation with Turkey, the Islamic State will seize the opportunity to rebuild.
The Syrian government and its primary allies, Iran and Russia, would also welcome a U.S. pullout from Syria. Iran would celebrate the reduced pressure on its presence there, particularly on its vulnerable supply lines in eastern Syria. Meanwhile, the Syrian government would likely attempt to reclaim the territory that the United States vacates, regardless of whether it would mean directly clashing with the SDF. After a U.S. departure, the SDF would likely attempt to strike a deal with Damascus.
The United States could lose credibility as a reliable ally if Washington suddenly withdraws, leaving its partners in the SDF open to an attack from Syria or Turkey. Washington has invested significant resources and time into building ties with the SDF and providing support for the organization. Moreover, Washington has repeatedly promised not to abandon its Kurdish allies in Syria. If the United States chooses to walk back that promise, onlookers in the Middle East and beyond could lose trust that the United States will stand by its commitments and may search for alternative partners. If the United States chooses to leave Syria, Russia, Iran and others will be all too eager to fill the space Washington leaves.