Bret Stephens has a strange idea about how no-fly zones work:

Use naval assets to impose a no-fly zone over western Syria, including Aleppo, Syria’s largest (and most embattled) city. A U.S. threat to shoot down Syrian military aircraft, including helicopters, will keep the Syrian air force grounded without requiring the U.S. to destroy Syria’s sophisticated anti-aircraft capabilities.

Destroying Syrian air defenses is essential to creating a no-fly zone. A no-fly zone cannot be enforced successfully without doing this. A no-fly zone can’t be imposed until after that has been done. Doing that means that the U.S. must start a war against the Syrian government.

Stephens’ comment is worth noting for a few reasons. It reflects a persistent, widespread misunderstanding of what no-fly zones are. Some people conflate no-fly zones with much more aggressive air campaigns that target ground forces, and others treat them as magical zones of protection that will somehow prevent ground attacks on vulnerable populations. There are some advocates of a no-fly zone in Syria that know what they’re talking about, but they are the exception. Threatening to shoot down Syrian aircraft while failing to create the conditions necessary to do that is nothing more than a bluff that would soon be called. The remark also represents the interventionist habit to pretend that starting wars against other governments is a low-risk move, which usually involves ignoring or denying the risks that would actually be involved. According to Stephens, the U.S. can dictate what happens in Syria’s airspace without first controlling it.

Last week, Gen. Dempsey explained that destroying Syrian air defenses was possible, but that it would require a longer, more difficult effort than we saw in Libya:

Army Gen. Martin Dempsey, who is chairman of the Joint Chiefs of Staff, says sorties over Syria are a daunting but feasible prospect, and doubts the virtue of the likely outcome.

“The U.S. military has the capability to defeat that system, but it would be a greater challenge, and would take longer and require more resources” than in Libya, Dempsey said during a lunch meeting with reporters.

“The air defense picture in Libya is dramatically different than it is in Syria,” he said. “Syria has five times more air defense systems, some of which are high-end systems, that is to say higher altitude, longer range.”

The real issue is that a no-fly zone commits the U.S. to a war in Syria, but it achieves none of the main things that interventionists claim to want:

A no-fly zone would be militarily effective, Dempsey said, though it likely won’t produce the kind of outcome that members of Congress or the American people would desire, such as an end to the violence, political reconciliation and stability in the country and region.

Of course, if the U.S. did impose a no-fly zone it would be just one of the first steps in our gradually escalating role in Syria’s conflict.