This piece is part of the Global Dynamics of the Syrian Conflict series, in which Carnegie experts from all over the world analyze the strategic and geopolitical interests at play in the ongoing civil war. View the full series here.

The conflict in Syria is affecting three core U.S. interests in the Middle East—the security of U.S. allies, the defeat of terrorists who threaten Americans, and the prevention of the development or use of weapons of mass destruction. Neighbors Jordan, Lebanon, Iraq, and Turkey have already been negatively affected, and Israel might be at some point. Syria has become a major hub of jihadi terrorism that threatens to turn on Americans as well as U.S. allies in the region and in Europe. And weapons of mass destruction have been used to devastating effect against Syrian civilians. In time, the conflict might also affect the fourth core U.S. interest—the free flow of oil from the region.

When U.S. President Barack Obama took office in 2009, his initial strategy toward the Middle East involved an effort to improve relations with Syria, including negotiations for peace between Syria and Israel. Had the effort succeeded, it could have given the United States a strategic advantage by prying Syria out of Iran’s orbit as well as bolstering Israeli-Palestinian peacemaking. The Syrian uprising that began in spring 2011, however, swept away this U.S. approach, as the brutal response by Syrian President Bashar al-Assad’s government to demonstrations soured U.S.-Syrian relations.

While the negative impact of the ensuing Syrian conflict on U.S. interests seems obvious, what to do about it has been less so, leading to much controversy inside the U.S. government and between the United States and its allies in the region. From the beginning, Obama has maintained that the United States could best protect its interests by staying out of the conflict as much as possible, a position that has been at odds with the assessments of others within his administration at times. Former U.S. ambassador to Syria Robert Ford acknowledged to Christiane Amanpour in a June 3 interview that he resigned because “I was no longer in a position where I felt I could defend the American policy.” He added that it was “now widely known that the State Department thought we needed to give much more help to the armed opposition in Syria.”

The United States has gradually been drawn into playing a greater role in supporting Syrian rebels, although it might be doing this more out of a desire to appease Saudi Arabia or resist Russian influence than to help Syrians. It is not possible to prove counterfactually that U.S. interests would have been better served—that allies would have been less destabilized by spillover from the conflict, that fewer and less heavily armed jihadi terrorists would be in the region, and that fewer WMD would have been used—if the United States had acted earlier and more decisively. What seems clear, however, is that U.S. reluctance to take a leadership role has contributed to a situation in which the Assad regime and its supporters (Russia, Iran, and Hezbollah) are far more cohesive and determined than the opposition and its supporters (Saudi Arabia, the Gulf states, Turkey, Europe, and the United States). That, in turn, has greatly increased the threat to core U.S. interests.

As the Syrian conflict has evolved, so have Washington’s policy responses. The United States principally used rhetoric and sanctions against the Syrian government in the first year or so of the conflict, shifting to more active diplomacy in 2012 and 2013. Then it gradually transitioned to covert and then more overt supply and training of rebels in 2013 and 2014.

All along, Obama and other senior U.S. officials have put forward a changing rationale for limiting U.S. involvement. In the first months after demonstrations broke out in March 2011, U.S. officials stated with confidence that Assad would and should fall from power just as leaders in Tunisia, Egypt, and Yemen had done in the face of similar uprisings. Washington also ramped up economic sanctions against his government. By late 2011, after the Syrian government’s harsh measures against peaceful demonstrations led to an armed insurrection, U.S. officials found themselves arguing that becoming more involved in Syria would prolong rather than end the conflict. That stood in contrast to the arguments they had made regarding intervention in Libya.

The United States took a more active diplomatic approach in 2012, still avoiding either military intervention or arming the rebels in the face of growing controversy in the United States, some of it related to Obama’s reelection campaign. Russia and China vetoed several draft resolutions in the UN Security Council but then in April agreed to a resolution on sending unarmed observers to Syria, part of a process that led to an agreement in June intended to pave the way for a negotiated political transition in the country. It soon became clear that the Syrian government had no intention of implementing the agreement, and as the fight heated up, U.S. officials began to express increased concern that the regime might use chemical weapons, leading Obama to draw a redline.

Obama’s reelection in November 2012 opened up space for a reexamination of U.S. policies, amid reports that most senior officials in his administration favored arming the rebels due to the skyrocketing human losses and refugee flows and escalating Iranian support for the Syrian government. As evidence mounted during spring 2013 that the Syrian regime was using chemical weapons against its own citizens, the United States began to supply at least small arms to the rebels and to coordinate with its allies in the Gulf to vet rebel units for larger arms. But arms deliveries were slow and cumbersome, partly due to U.S. concerns that the weapons would fall into the hands of Islamic extremist groups such as al-Qaeda offshoot Jabhat al-Nusra, which had been slowly building up its presence in Syria throughout 2012 and 2013.

As the Syrian conflict metastasized, the United States began to offer assistance to regional allies. It provided additional military and economic aid to Jordan, Turkey, and Lebanon, and gave Iraq missiles and drones. But it did not address the conflict directly.

The chemical weapons attack that killed more than 1,400 Syrians in August 2013 was a critical juncture. But Obama’s decision to defer to Congress on whether to strike Syria after the attack made clear that even under such extreme circumstances, he would not authorize any U.S. intervention in Syria. The president’s reluctance to use military force in a preemptive way certainly played a major role in this decision; he was also, perhaps, hesitant to antagonize Iran on the cusp of what seemed to be promising talks on the country’s nuclear program.

Instead of a strike, a diplomatic push ensued, producing an accord that led to the eventual removal of many chemical weapons but not to any lessening of the carnage. A second Geneva peace conference in January 2014 was a diplomatic debacle. And in spring 2014 the Syrian regime—with the strong support of Iran and Hezbollah—began to regain ground militarily against the rebels, leading to a reported U.S. decision to facilitate the covert transfer of antitank weapons that rebels had been requesting for nearly three years.

Washington’s decision to arm the opposition might have helped the rebels win their fight against the regime in 2011 or 2012. But now the hope is not that they can win—indeed, U.S. officials have long been ambivalent about a rebel victory, fearing it would only pave the way to a protracted struggle among rebel factions. The hope is simply to put enough pressure on the Syrian government to motivate it to engage in serious negotiations.

The U.S. assistance may be both too little and too late, however. The scenarios that now seem more likely to pan out include years of more fighting or the Assad regime’s gradual reestablishment of control over much of the country. Either outcome would be harmful to U.S. interests.

Continued fighting is likely to lead to strengthening and proliferation of jihadi groups, which already embrace a narrative of Western betrayal and are likely to use violence against U.S. or European targets at some point. Survival of a revanchist Assad regime would be little better for Washington and its allies, and indeed the last two years have proven that the two outcomes of regime survival and jihadi proliferation are not mutually exclusive. In view of the carnage Assad has perpetrated, the United States is unlikely to reconcile fully with him, but it might tolerate his survival in power unhappily and with a sense of unfinished business, as happened with Iraq’s Saddam Hussein after his invasion of Kuwait.

Having eschewed involvement in Syria out of fatigue at the human and financial costs of a decade of war in Iraq and Afghanistan, Americans might well in time come to see this choice as having been more costly to U.S. interests than anticipated.