Speaking from the White House on Thursday night about his decision to use U.S. warplanes to airlift humanitarian aid to thousands of Yazidis trapped on a mountaintop in northern Iraq, and, where necessary, to launch airstrikes against the Islamic militants who are besieging them, President Obama stressed that the military operation he had ordered was a strictly limited one. “I will not allow the United States to be dragged into fighting another war in Iraq,” Obama said.

There can be no doubt about Obama’s intentions. Even with ruthless fighters from the Islamic State in Iraq and al-Sham (ISIS) overrunning large parts of northern Iraq, the President has clearly demonstrated in recent weeks that he is deeply reluctant to use U.S. firepower in an effort to halt their advance. Spurning calls from the Iraqi government, and from the Kurds, to shore up American forces and carpet bomb the militants, he instead dispatched a few hundred military advisers to Iraq, saying that they’d assess the situation and report back. (George Packer has written about the people fleeing ISIS, and Dexter Filkins has urged American military support.)

Since then, the ISIS advance has continued unabated. Earlier this week, they seized control of Iraq’s largest dam, which is north of Mosul on the Tigris, and its biggest Christian settlement, the town of Qaraqosh. Today, the group is within striking distance of Erbil, the capital of the Kurdish region. Even now, though, instead of stating that enough is enough, and that it’s time for the U.S. military to arrest ISIS’s advance, the President cast the coming mission as a humanitarian one, saying: “When we face a situation like we do on that mountain—with innocent people facing the prospect of violence on a horrific scale; when we have a mandate to help—in this case, a request from the Iraqi government—and when we have the unique capabilities to help avert a massacre, then I believe the United States of America cannot turn a blind eye. We can act, carefully and responsibly, to prevent a potential act of genocide.”

Actually, though, the American intervention is not a wholly humanitarian one. In addition to ordering the Pentagon to deliver food and water to tens of thousands of Yazidis, a Kurdish religious group whose members are braving the elements on Sinjar Mountain, near the border with Syria, Obama authorized airstrikes on ISIS forces if they continue their advance toward Erbil. But there’s not much of an “if.” Ever since they captured Mosul, Iraq’s second-largest city, a couple of months ago, the militants have been moving slowly but steadily south and east, toward the Kurdish capital. It seems highly doubtful that they will stop now. This means that U.S. warplanes are likely to be engaged on at least two fronts: in the northwest, protecting the Yazidis and the U.S. military transport planes that will deliver the humanitarian assistance; and in the northeast, engaging the ISIS fighters between Mosul and Erbil.

On Thursday evening, Kurdish officials said that U.S. airstrikes had already begun. The Pentagon firmly denied this, suggesting that the forces of the Iraqi government, or of neighboring Turkey, may have carried out some bombing raids. However, even if U.S. warplanes haven’t yet engaged ISIS positions, it seems that it will be only a matter of time before they do. The Pentagon already has plenty of firepower in the region. According to a report from NBC News, the U.S. military has been flying B-1 bombers, F-18 attack aircraft, and MQ-1 Predator drones over Iraq for several weeks.

Once the U.S. bombing starts, when will it stop? That is one of the many tough questions that Obama and his colleagues will have to answer. Are the sole goals of the mission to help out the Yazidis and prevent Erbil from falling? Or is this the beginning of a U.S.-led effort not merely to halt the advance of ISIS on its eastern front, in the Kurdish region, but to roll it back everywhere in the country?

On these questions, Obama was studiously ambiguous. “Even as we carry out these two missions, we will continue to pursue a broader strategy that empowers Iraqis to confront this crisis,” he said. Rather than dwelling on what role the U.S. military might play in such a strategy, he called for action from Iraq’s politicans, who are currently trying to form a new government and, possibly, select a new Prime Minister to replace Nouri al-Maliki. (A couple of months ago, Dexter Filkins Profiled Maliki in the magazine.) “Iraqi leaders need to come together and forge a new government that represents the legitimate interests of all Iraqis, and that can fight back against the threats like ISIS,” Obama said. He went on, “Once Iraq has a new government, the United States will work with it and other countries in the region to provide increased support to deal with this humanitarian crisis and counterterrorism challenge.”

Given the snail’s pace at which Iraqi politicians move, Obama clearly isn’t going to rush into expanding the mission. Already, though, one Rubicon has been crossed. A President who came into office on a promise to pull the United States out of Iraq, and who followed through on his pledge, has just ordered more combat operations in, or over, Iraq.