How many innocent Syrian civilians would be killed should the United States launch airstrikes against Syrian government radars, antiaircraft sites and air bases — obvious targets if the White House approved setting up the no-fly zone some members of Congress want? What would be the legal basis for such action?

These questions emerged last week as I listened to a Senate Judiciary subcommittee hearing devoted to the constitutional and counterterrorism implications of targeted killings by drones — unmanned aircraft. The countries mentioned were Yemen, Pakistan and to some degree Afghanistan.

Syria never became a focus because President Bashar Assad’s military has advanced Russian fighter planes and air defense weapons. They make it impossible to use slow-flying drones, which can easily be shot down by relatively low-tech anti-aircraft weapons. The hearing did focus on civilians killed by remotely piloted aircraft and the resultant fear and anger.

But the testimony drew distinctions between the use of manned aircraft, which would have to be the case in Syria, and the drones that have drawn so much criticism as used in Pakistan, Yemen and elsewhere.

Martha McSally, a retired Air Force colonel, said the remotely piloted aircraft “has the advantage that it is an ISR (intelligence, surveillance and reconnaissance) and strike platform and can loiter overhead around the clock to ensure all strike criteria are met.” Collateral damage is minimized because normal miss distances are “less than 10 feet.”

Once the drone is chosen for a legal strike, McSally said, unlike manned aircraft, commanders, intelligence analysts and legal experts monitor the operation and provide the “ability to abort the strike if the target moves or civilians enter the area.” Another benefit: immediate poststrike assessments.

Without mentioning Syria, McSally drew comparisons between the use of drones and fighter-bombers. Manned fighter-bomber strikes need actionable intelligence and “the lead time required to plan, brief and travel to-and-from the target area.” In the case of Syria, there would be a potential requirement for diplomatic overflight clearances, air refueling support and airborne command and control, which she said are necessary “to provide real-time updates, clearance to strike and abort decisions.” If there is no real-time intelligence, McSally said, the final strike decision for fighter-bombers “is made by the pilot in command.”

The Authorization for Use of Military Force (AUMF), a joint resolution passed by Congress on Sept. 14, 2001, was first used by the George W. Bush administration, and now by President Barack Obama, to authorize the use of drones in counterterrorism operations. It gives the president authority to “use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the attacks that occurred on Sept. 11, 2001, or harbored such organizations or persons, to prevent any future acts of international terrorism against the United States by such nations, organizations, or persons.”

According to a subcommittee witness, Georgetown University Law Center professor Rosa Brooks, “AUMF’s language appears to restrict the use of force both with regard to who can be targeted — those with some culpability for the 9/11 attacks — and to the purpose for which force is used — to prevent future attacks against the U.S.”

A former counselor during the first two years of the Obama administration to the undersecretary of defense for policy, Brooks said that drone strikes have evolved “from a tool used in extremely limited circumstances to go after specifically identified high-ranking al-Qaida officials to a tool relied on in an increasing number of countries to go after an eternally lengthening list of putative bad actors, with increasingly tenuous links to grave or imminent threats to the United States.”

So what legal basis would be used for a military strike in Syria?

The drone strikes in Yemen are openly authorized by that country’s government. In Pakistan there is a less public wink-and-nod approach, though the AUMF clearly applies to al-Qaida and Taliban targets.

What imminent threat to the United States does the Assad regime pose? You could try to argue that the radical jihadists supporting the opposition to Assad have some distant al-Qaida ties. But wouldn’t the U.S. bombing be supporting them in a joint effort to end Assad’s regime?

What about U.S. participation in a no-fly zone in Libya based on humanitarian needs? Doesn’t work. The legal basis for that no-fly zone was U.N. Security Council Resolution 1973, adopted March 17, 2011, which imposed “a ban on all flights in the airspace of the Libyan Arab Jamahiriya in order to help protect civilians.” The Security Council also authorized member states who have notified the Security Council and League of Arab States, acting nationally or through regional organizations, “to take all necessary measures to enforce compliance.”

The reference to “all necessary measures” is “the standard phrase the Security Council uses to authorize states to act militarily,” according to a Yale Journal of International Law Online article by Michael N. Schmitt, a former professor of international law at the U.S. Naval War College. There’s no such resolution for Syria. Without one, or without Congress approving a Syrian resolution, there is no legal basis for U.S. forces striking Syrian targets.

Walter Pincus reports on intelligence, defense and foreign policy for The Washington Post.

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