Until recently, one of the arguments employed by those who oppose a greater American role in stopping the slaughter in Syria has been that Bashar al-Assad’s forces were closely intermixed with the population and that it would be hard to hit the regime’s thugs without also hurting innocent people.

But news that Assad is relying more on helicopter gunships—which, according to Secretary of State Hillary Clinton, he continues to receive from Russia–actually creates a vulnerability that could be exploited at relatively low cost by sophisticated Western air forces.

Helicopter gunships are formidable when deployed against civilians; but they are sitting ducks if they have to face fixed-wing fighters such as the F-15 or F-18. If the U.S. and its allies were to declare a no-fly zone over Syria, it would hardly end the violence. But if NATO aircraft were thereby authorized to, at a minimum, ground Assad’s helicopters, that would certainly strike a blow against his campaign of terror and help put the rebels on a more equal footing with the government.