U.S. President Barack Obama has taken pains to avoid being drawn into Syria’s civil war. He does not appear convinced that the United States has sufficient strategic interests in Syria to warrant—let alone sustain—another long-term commitment of military force to shape the outcome of what is a complicated and many-sided struggle. Even as Obama has expanded the U.S. war against the Islamic State of Iraq and al-Sham (ISIS) to include targets in Syria, then, he has tried to circumscribe the mission. The aim is to battle ISIS without either aiding or fighting the regime of Syrian President Bashar al-Assad. But the balancing act is proving difficult. The United States could soon face a choice between appearing to provide tacit support to Syrian government forces and joining the fight against them.

The United States has long faced pressure to intervene in Syria’s civil war; it dates back to 2011, even before early skirmishes turned into high-intensity combat. Then as now, the administration’s stance was cautious. At that stage, it looked as though Assad might go the way of Tunisia’s Zine el-Abidine Ben Ali or Egypt’s Hosni Mubarak. Given the brittleness of the Assad regime, the use of force seemed unnecessary. And in any case, there was no appetite for a bidding war with Iran for Syria.

Yet the Assad regime proved more resilient than many expected. Interest in arming and training the Syrian rebels only grew, despite Washington’s evident inability to wield influence over the hundreds of partially radicalized armed groups already proliferating in Syria, let alone mold them into a unified opposition army. As we now know from multiple memoirs, Obama overruled his secretaries of defense and state, who urged him to do more to arm those rebels in late 2012.

Calls to help overthrow Assad grew louder after his regime used chemical weapons against civilian populations in August 2013. Again, Obama declined to strike once the United Kingdom opted out of military involvement and Russia proffered a diplomatic alternative that eventually stripped the regime of its chemical weapons. The resulting mix of disappointment and anger at home over a forgone opportunity to strike Assad’s forces was bound to make it harder for Obama to say no the next time a challenge arose.

And it did. Following reports that ISIS, which had just overrun the western provinces of Iraq and entered Mosul, was intent on the genocide of a religious minority in Iraq, the United States immediately launched air strikes to protect the vulnerable and safeguard American officials in Erbil. The use of force never comes without unintended consequences, and in this case, the attacks precipitated the murder of two Americans, which in turn amplified calls for military escalation.

Even so, in that early phase of U.S. military operations, the air campaign was in the service of a clear, if limited, interest in protecting the American strategic investment in Iraq by relieving jihadist pressure on Baghdad and pushing the divisive prime minister, Nouri al-Maliki, out of office. To the extent that prospective strikes in Syria were discussed, their narrow aim was to deprive what was seen as an Iraqi insurgency of its sanctuary across the border. As the objective expanded to include the destruction of ISIS, though, U.S. strikes have extended as far west as the outskirts of Syria’s former cultural and economic capital of Aleppo, now a vast rubble field contested by the regime and a congeries of rebel militias, and as far north as the Turkish border.

These attacks, with their implied promise of close air support for non-jihadist fighters assailed by ISIS, have brought the United States perilously close to entry into the Syrian civil war. Turkish Prime Minister Ahmet Davutoglu’s recent offer to send Turkish troops into Syria if the United States would, in return, directly attack the Assad regime—and Ankara’s wrangling with the United States over access to Turkish air bases—has only added to sustained pressure coming from the Gulf allies.

The key question is: What happens if one of the non-jihadist opposition groups that the United States is aiding in the fight against ISIS requests urgent assistance against the Assad regime? If the United States fails to come to the group’s aid, the support the United States enjoys among these groups by virtue of its airpower and train-and-equip efforts would swiftly fade. But if the United States accedes to the request, then it unequivocally becomes a combatant in the civil war. And if the United States consents to Turkey’s proposal for a safe haven within Syria for refugees and possibly as a base for an opposition army—essentially a tethered goat stratagem designed to trigger regime attacks that American planes would then have to repel—Washington would become even more deeply engaged in the conflict.

The civil war in Syria does, of course, endanger some U.S. strategic interests. Iraq, for example, is one, and the United States has acted decisively to protect it. Jordan is another, given the Hashemite Kingdom’s historically close relationship with the United States (it is a Major non-NATO Ally) and its close security links to Israel. The influx of Syrian refugees into that country is a threat to its stability, as is the receptive audience ISIS has found among the unemployed youth in its impoverished desert cities. In response, the United States ramped up its already considerable economic and military aid to Jordan and, last December, deployed 6,000 soldiers to Jordan for a large-scale exercise. Likewise, Lebanon has received billions in military aid from Riyadh, while Hezbollah fields a force that has faced the Israeli army on the battlefield and is ideologically primed to contest ISIS attempts to establish a beachhead in Lebanon. And between 2012 and now, the United States has provided nearly $3 billion in humanitarian aid for displaced Syrians.

But there is no equivalent U.S. interest in Syria per se. For 40 years, it was a strategic ally of the Soviets; it then switched its allegiance to another strategic adversary, Iran. Most Syrians are skeptical of U.S. intentions, owing to decades of support for Israel as well as the United States’ hands-off approach to the civil war. Assad’s outreach to Washington, which came only a short time before rebellion broke out, was too little, too late. There is no history of cooperation, shared causes, or solemn commitments. Syria is of no military value to the United States, which has ample basing and access options throughout the Mediterranean rim, and of negligible economic value.

It would be strategically useful to completely deny Syrian territory to Iran, but the attempt to do so would likely increase Iran’s military involvement and heighten sectarian tensions, while complicating efforts to reach a deal on Iran’s nuclear program. Although some terrorist attacks in the West, such as the one just carried out in Canada, will certainly arise from a jihadized Syria, the long-term investment the United States has made in homeland security and intelligence programs, combined with air strikes that keep ISIS conspirators in Syria and Iraq off balance, should contain the problem without the burden of a new expeditionary commitment.

Hence the administration’s dilemma. On the one hand, military intervention in the civil war would commit the United States to an expensive and ongoing enterprise unrelated to a strategic interest in Syria itself. On the other, it might prove necessary in order to bring other countries’ firepower to bear against ISIS. While Washington debates the question, however, its air operations deep in Syrian territory could propel the United States into the civil war without a considered or explicit decision.

A tragic choice is emerging between restraint against ISIS to avoid entanglement in Syria’s civil war or full engagement against ISIS with an eye to regime change and the reconstruction and stabilization of a devastated country. After Afghanistan, Iraq, and Libya, we have a rough idea of what such an effort would entail and of the elusiveness of lasting gains. A decision to go all the way is one that should be taken only with the greatest of caution and a careful assessment of the gap between our resources and our maximalist goals and the gap between these goals and our strategic interests. At this stage, all these considerations remain badly out of sync and quite possibly irreconcilable.