President-elect Trump has stated his intention to strengthen the U.S. approach to defeating the Islamic State (ISIS). However, the precise way in which his administration will pursue this objective is still taking shape. While ISIS has inspired attacks and spawned a number of affiliates globally, the central and immediate challenge resides in Syria and Iraq, at the heart of ISIS’ so-called caliphate. Iraqi security forces, supported by the anti-ISIS Coalition, have succeeded in removing ISIS from 56 percent of the territory it occupied there in 2014, and U.S.-backed Syrian opposition forces have further constricted ISIS in northern Syria. Yet, the burgeoning campaigns to retake ISIS’ strategic strongholds in Mosul, Iraq and Raqqa, Syria will be hard-fought. Harder still will be consolidating the gains of these campaigns to ensure that ISIS—or likeminded groups—are unable to regrow, and enabling enduring political solutions in Iraq and Syria to prevent future terrorist groups from taking root. The United States will need a strategy that synchronizes the right mix of military forces and non-kinetic tools to achieve this outcome.
Americans have no interest in perennial military interventions in the Middle East. The United States has competing geostrategic objectives in Europe and Asia and demands for resources at home. However, the United States has compelling reasons to not only defeat ISIS but also to address the broader factors that have enabled ISIS’ rise. Additionally, the United States has to contend with intertwined regional realities that could challenge its ability to negotiate and influence outcomes to its advantage. Among these reasons are: countering terrorists and the roots of terrorism, which threaten the U.S. homeland and our allies and partners; preventing military confrontation with Russia and Iran while limiting the long-term, subversive influence they could have in the region; and stemming conflict emanating from Syria and Iraq from further destabilizing neighboring states and Europe.
At its height in 2014, ISIS reportedly possessed more than 30,000 forces. U.S. and Coalition operations in Iraq and Syria have since degraded ISIS to approximately 17,000 fighters by the end of 2016, through local partnered operations and direct attacks. President Obama authorized over 4,600 U.S. forces to advise Iraqi security forces in their push to eradicate ISIS.1 By the end of December 2016, the multinational anti-ISIS Coalition had conducted airstrikes against 31,900 ISIS targets. In addition, Iraqi Kurdish Peshmerga militias regularly partner with anti-ISIS efforts in northern Iraq. Operating separately from the Coalition but with the common purpose of defeating ISIS, Iraq’s Popular Mobilization Forces (PMF) now number roughly 100,000, partnering with Iraqi security forces. Iran provides direct support to roughly 80,000 of the PMF, providing Iran with substantial leverage over Iraq’s future. In late December, Iraqi security forces reinitiated a push on Mosul—Iraq’s second largest city and key ISIS stronghold.
The United States has authorized 500 special operations forces (SOF) personnel in Syria, partnering with 40,000 to 50,000 Syrian Democratic Forces (SDF). The SDF is comprised primarily of Syrian Kurdish forces such as the People’s Protection Units (YPG) to fight ISIS and the al-Qaida affiliate Jabhat Fateh al-Sham (JFS). Together with U.S. SOF in Syria, these units successfully pushed ISIS and other extremists out of most of northern Syria in 2016, although substantial governance and security challenges remain. For one, the YPG is affiliated with the Kurdistan’s Workers’ Party (PKK), deemed a terrorist organization by Turkey. Turkey’s intervention in northern Syria has complicated U.S. and allied security efforts, as U.S. and Turkish objectives clash with regard to the role and reach of the YPG. Additionally, Arab-Kurd tensions present the specter of a civil war to come. Backed by U.S. SOF, the operationally effective and predominately Kurdish SDF is currently sweeping the countryside surrounding ISIS’ capital in Raqqa; however, they are not prepared to address the governance and security challenges that will inevitably arise after the initial push into the predominantly Arab city.
Additionally, Russia currently has 4,000 troops in Syria. Its intervention in 2015 has since enabled the Syrian government to reinforce its positions, retake territory from Syrian rebels, and regain Aleppo, using brutal tactics against Syrian civilians and targeting hospitals and schools. Assad’s Syrian Armed Forces currently fields close to 300,000 troops. Buttressing Assad’s forces, Iran has mobilized up to 115,000 fighters in Syria, comprised of Lebanese Hezbollah, Syrian, Iraqi, Afghan, and Pakistani recruits. Taken together, there is a significant fighting force with active supply lines from external allies backing Assad. With Aleppo largely secured, the Assad-Russia-Iran alliance is now turning to other areas of the country to crush all Syrian opposition, including not just ISIS and JFS, but also groups backed by the United States and its regional Arab partners. Russia and Turkey recently brokered a temporary ceasefire with non-ISIS and JFS Syrian opposition groups ahead of peace talks scheduled in Kazakhstan later this month, but as with previous ceasefire attempts, reports of Assad’s forces targeting opposition-held areas continue, and the prospects of the ceasefire holding grow dim.
Within this complex mix of international forces and differing objectives, the Trump Administration will face several operational challenges to address the narrower but related goal of defeating ISIS. While the current anti-ISIS strategy has strong overt and covert lines of effort, there are areas where these initiatives are not sufficiently coordinated to sequence and maximize effects. While ramping up airstrikes alone could dramatically increase the number of ISIS targets destroyed, the Trump Administration will quickly realize the limits of airstrikes without complementary ground forces to reinforce gains. However, local partner limitations, driven by capacity and credibility shortfalls and misalignment with U.S. objectives, will likely continue to plague anti-ISIS efforts. In addition, operational planning for the Mosul and Raqqa campaigns have been necessarily segregated due to U.S. government legal authorities and local and national-level partner dynamics (i.e., the United States can work with Baghdad but has no national partner in Syria). This lack of synchronization risks allowing ISIS to exploit gaps in the two campaigns, and flow personnel, arms, and supplies more easily across the non-existent Syria-Iraq border.
At the strategic level, several challenges loom. The current under-emphasis on consolidating gains from counterterrorism operations risks the rise of another iteration of ISIS in five years. Russia and Iran have seized opportunities in Syria—and Iran even more so in Iraq—to deepen their influence and leverage in ways that run counter to long-term U.S. interests, and the security of Israel and regional Arab partners. Finally, despite increased targeting and coordination to pressure JFS in the past year, an exclusive emphasis on ISIS could allow JFS to opportunistically fill a security and governance void if other local and credible actors do not step up.
The incoming Administration should consider several factors while navigating these challenges. First, solely strengthening counterterrorism efforts risks overlooking need to consolidate gains as local and Coalition forces clear areas. Second, partnering with Russia and Iran—or Assad—could accrue short-term gains to degrade ISIS, but risks tradeoffs to long-term stability and governance in Syria and Iraq, as well as to U.S. influence in both countries and with regional partners. Finally, pacing and sequencing a counterterrorism approach in the Syria and Iraq region to defeat and ISIS and JFS requires a strategy that depends upon both local and cross-regional coordination, although U.S. tools and level of emphasis are often applied at national level.
Considering these challenges, the Trump Administration should implement the following changes to strengthen the counter-ISIS strategy:
- Forge a common and coordinated political and military approach with allies and partners for Syria and Iraq, countering terrorism and its underpinnings. This may require an increased mix of both SOF and conventional ground forces, with U.S. conventional forces providing support to U.S. SOF conducting training and combat operations with local partners;
- Let operational conditions on the ground inform strategic adjustments and withdrawal timelines. ISIS will not be defeated in the next year; it will require a multi-year effort;
- Enhance intelligence-sharing and combined operations within the region and with European allies and partners to disrupt ISIS terrorist attacks, improving coordination among military, intelligence, and law enforcement entities;
- Increase focus on consolidating gains from ground and air operations, setting the conditions now for what comes after ISIS and JFS by amplifying support to and knitting connections among local security forces and governance structures in both Syria and Iraq.
- Determine if new authorities and tools are needed to provide funds and support to local security and governance actors and work with the U.S. Congress to develop them;
- Strengthen operational planning and coordination across Syria and Iraq, synchronizing operations for Raqqa and Mosul to squeeze ISIS, and aligning covert and non-covert approaches versus ISIS and JFS;
- Set redlines for Russian and Iranian behavior and be prepared to enforce them (e.g., removing the long-term presence of IRGC-backed groups in Syria and Iraq); and
- Work with the international community to provide emergency humanitarian assistance to besieged areas, with clear and immediate repercussions in the case of outside interference. Beyond the compelling moral imperative to do so, generations of Syrians and Iraqis will remember potential U.S. inaction, which could feed extremist anti-U.S. narratives and boost terrorist recruitment.
 This estimate does not include troops in theater for rotational training assignments, civilians, and contractors.