To stop the regime’s assault, let alone to topple it, would have required direct military pressure, most likely a massive air and missile campaign and probably an intervention force. Those, quite rightly, were never under serious consideration. Half-measures such as arming the rebels and instituting a “no-fly” zone carried risks but no identifiable rewards. It was never clear how a limited military response would shape events. U.S. planners could not be certain that a military response wouldn’t have pushed Russia and Iran to up the ante with more weapons. And with Washington seeking Moscow’s support to keep pressure on Iran’s nuclear program, a major escalation over Syria wouldn’t have helped.

And who, exactly, would we have been arming? Once the United States backs a particular rebel group, Washington would be responsible for its actions. Neighbors such as the Saudis and Qataris may have a stake in arming Sunni fundamentalists in Syria, but the United States does not. As for the Turks, the Obama administration did not prevent Prime Minister Recep Tayyip Erdogan from acting militarily. Erdogan faced serious internal constraints: Neither the general public nor 15 million Turkish Alevis aligned ethnically with Syrian Alawites wanted war with Damascus…

We will never know about the “what ifs” had the United States intervened in a more aggressive way. But to blame the arc of this crisis on Washington or to suggest that the Obama administration made it worse fails to understand the cruel nature of the Syrian tragedy and the limits of U.S. power and our national priorities. The United States is coming out of the two longest wars in its history, in which the standard for victory was never “can we win?” but “when can we leave?”