How many innocent Syrians should we be willing to kill to send a message? Since Barack Obama feels the need to make a point about chemical weapons and sees verbal options as inadequate, that's the question we confront. But it's hard to think of a number that is easy to justify.
Killing civilians is an inevitable part of war. But wars are usually fought for big, vital purposes: to assure a nation's survival, protect its independence or eliminate some horrible evil. The attack Obama apparently has in mind for Syria, however, is something short of full-scale war, and it lacks a tangible objective.
He is expected to send cruise missiles against military units and installations. The idea is not to blow up Syria's chemical weapons, which could rain toxins on the local population. The idea is to prevent their use by raising the cost to President Bashar al-Assad.
Another motive is to confirm the credibility of Obama, who had vowed to retaliate if the regime used chemical weapons. This demonstration is supposed to impress not only Syria, but Iran, as it considers whether the U.S. would use force to keep it from getting nukes.
The anticipated strikes, we are told, will be strictly limited. Obama is not trying to topple the regime, enable the rebels to win or force Assad to negotiate. His aims are more abstract: enforcing accountability and promoting deterrence.
But the attack may well achieve neither. Assad could absorb the blow, decide he can take what the U.S. is willing to dish out and use these agents again. Or he could revert to conventional methods of slaughter, which have been adequate to kill more than 100,000 Syrians.
If Assad does not respond as hoped, Obama will face an unhappy choice: admit failure or take bigger, riskier actions to get his way. Having upheld his credibility, he may be forced to uphold it again. Credibility, you see, is highly perishable.
It's also not readily transferable. For Obama to follow through on his threats in Syria doesn't guarantee he'll follow through elsewhere.
Kori Schake, a national security analyst at Stanford's Hoover Institution, scoffs at the notion that hitting Syria will deter Iran. "I certainly don't believe cruise missile strikes will achieve that, because it would take a sustained military campaign to destroy Iran's nuclear programs, and the president keeps conveying -- in Iraq, in Afghanistan, in Libya and in Syria -- that he isn't willing to fight one," she told me.