A ‘red line’ on Syria

President Obama has followed a commendably restrained policy in refusing to intervene militarily in Syria’s civil war. But if the U.S. confirms that the regime of President Bashar Assad has used chemical weapons, the president should adhere to his insistence last year that such conduct would be a “red line� justifying action by this country, alone or in concert with other nations.

That doesn’t mean the administration should accept uncritically suggestions by Israel, Britain and France that the regime has used chemical agents. As Secretary of Defense Chuck Hagel said Wednesday, “Suspicions are one thing; evidence is another.� But the administration should aggressively seek the intelligence necessary to decide whether action is required, and not wait passively for others to establish the facts.

Last week, France and Britain asked the United Nations to investigate what they called credible — but not definitive — evidence that the regime has used small amounts of chemical weapons in recent months. On Tuesday Brig. Gen. Itai Brun, Israel’s top military intelligence analyst, said that Syria used chemical weapons, probably a sarin-based nerve agent, in attacks on militants last month near Aleppo and Damascus. He said the assessment was based on pictures of victims foaming at the mouth and with constricted pupils.

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A U.S. defense official told The Times that Britain and France “did not provide conclusive evidence of chemical weapons use� in their request to the U.N., and the phenomena described by the Israeli general may be open to multiple interpretations.

Last August, even as he resisted the notion that the United States should intervene in Syria, Obama said that “a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus.� And so it should. Ever since the use of mustard gas in World War I, civilized nations and the international community have condemned the use of chemical (and biological) weapons, not only because they cause mass destruction but because of their cruelty.

Granted, conventional weapons also cause death and suffering — and have done so in Syria — but the use of chemical weapons would represent a reckless escalation of Assad’s war on his own people.

An American or multilateral response should of course be proportional to the offense. That means considering whether chemical weapons were used against civilians or militants, and whether a “whole bunch� were used, as Obama put it, or much less. But there’s no doubt that an operation to secure or destroy the regime’s chemical weapons would be consistent with this country’s stated commitment (one that all too often has not been honored) to protect civilians from the worst ravages of war.

Yes, the president must be sure before he acts; but if it is proved that Assad has crossed the “red line,� Obama must respond.