The awful things that could have happened had the United States intervened in Syria are now happening anyway. The insurrection has become a civil war. Neighboring countries are being dragged in. A refugee crisis has been created. Jihadists have entered the fray, and the death toll has passed 20,000. The worst has happened — maybe because the best did nothing.

Had Barack Obama committed the United States to get involved in a muscular fashion, the civil war in Syria might now be over. This, of course, is just a guess, open to the usual criticism and derision by foreign policy realists. But it is not all that unrealistic to presume that had the United States hit Syria’s command and control centers, the defection of generals and other officials would have become a stampede. Nothing so illuminates an exit sign as the certainty of defeat.

That certainty, predicted by just about everyone in the Obama administration for more than a year now, has somehow yet to come to pass. This is because the Syrian army has stayed with the regime of Bashar al-Assad not out of any love for him but because it fears the alternative. By letting the situation fester, the United States and its anti-Assad allies (Saudi Arabia, Turkey, etc.) have allowed the fight to become a sectarian one. The major rift in the Middle East is not between Israelis and Arabs but between Sunnis and Shiites. In this fight, Syria is becoming the latest battleground.

At the moment, planes are flying over Syria and dropping bombs. Unfortunately, they are Syrian military aircraft bombing their own people. This could be stopped. The United States, NATO and others under the rubric of Friends of Syria have the capacity to implement a no-fly zone — and to do it fast. Grounding Syria’s air force and helicopter gunships would not only aid the opposition but also send a strong message to the regime and its supporters that their days are numbered. As things stand, those days are not numbered, and the end is in doubt. For example, Aleppo has apparently been retaken by Syrian forces loyal to Assad.

It is true enough that the outcome of the civil war may not benefit the United States or, for that matter, Israel — even if it represents a black eye for Assad’s backer, Iran. If the mostly Sunni insurgents win, they may well impose an Islamist regime and turn, with ferocity, on the Shiites (and their allies, the Alawites) as well as the Christians, 10 percent of the population. And an Islamist Syria would be a more implacable foe of Israel’s than the secular Assad regime. The chances of this happening only improve the longer the war goes on and jihadists from all over the Islamic world join the fight. Time is not on our side.

The reluctance of the Obama administration to apply some muscle to its (mostly) rhetorical support of the Syrian opposition has only worsened matters. At first, the administration seemed to hope that the dreamy plan advanced by former U.N. secretary general Kofi Annan would work. Now, it is supplying communications equipment and, one would hope, some military and civilian advisers, but it has shied from imposing a no-fly zone or using air power to hit some strategic military and governmental targets.

The thinking is that Syria is a mess, a stew of mutually hostile ethnic groups. Moreover, its Russian-provided air defense system must be taken into account. As I have noted before, Israel took that system into account when it bombed a Syrian nuclear facility in 2007 — and got away with no loss of aircraft. If Obama had the will, the Pentagon could find the way.

Opponents of U.S. intervention say that the United States has no urgent reason to get involved in Syria. For the moment, they have a point. But the spread of the fighting will threaten neighboring countries — Jordan and Lebanon, in particular — and further destabilize the Middle East. In addition, the opportunity to end what amounts to slaughter ought to be seized. Someone has to tell thugs that they cannot save their skins by the wholesale murder of their own people. Exile is a better choice.

Already, the bad things that were predicted had the United States done something bold in Syria are coming to pass. More than 130,000 refugees have fled into neighboring countries, and civilians continue to die. Residential areas have been leveled by artillery and now by bombs. The opposition is calling for a no-fly zone. If anyone is calling the White House, that phone will ring and ring. When it comes to Syria, there’s no one home.