An agreement with Russia to renew efforts to negotiate peace in Syria bolsters President Obama's argument that now is not the time for a U.S. military role in the conflict.

Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov announced Tuesday in Moscow that an international summit would be held as early as this month to revive a plan that would effectively end Syrian President Bashar al-Assad's rule.

The announcement blunts the hawks' harsh criticism of Obama for backing away from his hasty declaration eight months ago that any use of chemical weapons by Assad would cross a "red line," leading to "enormous consequences." When Syrian hospitals began reporting admissions of patients with symptoms consistent with chemical-weapons poisoning, the White House retreated, suggesting that U.N. investigators should test patients' urine and soil samples for contamination to determine whether the line had really been crossed.

Obama's caution fueled further accusations of timidity by critics, who said it shouldn't take chemical weapons to get the United States more involved. "Unfortunately, the red line that the president of the United States has written was apparently written in disappearing ink," said Sen. John McCain (R., Ariz.).

But it's easy to play armchair quarterback when you won't be held responsible for the outcome, which McCain won't. Obama, on the other hand, won't be treated kindly by history if he puts his already war-weary nation smack dab in the middle of yet another conflict that - like Iraq and Afghanistan - has the scent of heading toward an unsatisfying end.

This country doesn't like sitting still when it could help topple a regime that would poison its own people to retain power. But figuring out how to assist beyond providing humanitarian aid isn't easy. Arming the rebels, some of whom are said to be members of al-Qaeda in Iraq, would risk letting weapons fall into the hands of groups hostile to the United States.

Before Kerry's trip to Moscow, some foreign policy experts were suggesting a regional conference chaired by the United Nations, which would include Iran and other Middle East nations as well as the five permanent U.N. Security Council members: the United States, Russia, China, France, and Britain. But there's no guarantee that such a conference would succeed.

An international conference in Geneva came up with a peace plan for Syria 11 months ago, but it went nowhere because the United States insisted that Assad resign as a precondition of talks. Kerry made no such demand Tuesday, however, so there is reason for optimism.

Russia's agreement to use its considerable influence with Assad to seek an end to the civil war vindicates Obama's reluctance to ratchet up the United States' role in it, which could take this country down another slippery slope to military intervention. The time may come for that, but it isn't now - and most Americans hope it's never.