One day, a decade or so down the line, an American president will call on the Putin of his time and propose an international conference to contain the sectarian and religious warfare then threatening their common interests in south-central Asia, a broad swath of land running from Afghanistan to Kazakhstan. The Russian leader, already absorbed with the festering Islamist challenges in Chechnya, Dagestan and other parts of the northern Caucasus, will reluctantly agree.

A similar scenario is now unfolding, though the immediate crisis centers on the killing fields in Syria, blood splattered for more than two years by Sunni-Shiite-Alawite-Kurdish violence. Two senior American officials recently visited the Kremlin, both appealing for a major, new effort at Russian-American cooperation to stop the spreading violence. National-security adviser Tom Donilon arrived first on April 15, coincidentally the day of the Boston marathon disaster, which for the first time introduced the roiling Islamic radicalism of Chechnya and Dagestan into the springtime pageantry of a New England tradition. Donilon carried a letter from President Obama to President Putin, proposing, among other things, a new international conference on Syria designed to negotiate a political transition from the Assad regime to something better. The “something better” was left vague, and therein lay a subtle but important change in American policy.

A few weeks later, on May 6, Secretary of State John Kerry arrived at the Kremlin with the task of translating the “change” for Putin and Foreign Minister Sergei Lavrov. Up to this point, the Obama administration had insisted that Assad had to go before a new Syrian regime could be formed. Now, Kerry explained, in a bid to win Russian approval, Assad could be represented at the proposed international conference, whose task would be the formation of a new Syrian government, but he would no longer play any role in the new government. His rebel opponents, supported by the United States and much of the UN, would not accept him. In this way, Assad would be gone, eased out of power by the manipulative magic of diplomacy rather than booted ignominiously out of his palace in Damascus.

At a midnight news conference with Kerry, Lavrov hinted broadly that the Kremlin could live with this revised American approach to Assad’s ouster. “We are not interested in the fate of certain persons,” said the Russian diplomat.

Much can yet happen to crush this new flowering of Russian-American cooperation. But much has happened in recent weeks to offer at least a flicker or two of hope that progress is now possible.

First, the reported use of sarin gas in Syria, the crossing of President Obama’s “red line.” Bear in mind that Putin’s insular foreign policy these days rarely goes beyond the suburbs of Moscow. The Russians instinctively imagined that their radical Islamist antagonists in the northern Caucasus would now be inspired to use chemical weapons against them, posing a direct threat to people in Moscow and St. Petersburg and possibly to visiting foreigners at the time of winter Olympics in the Caucasus next year. Putin may have the deepest reservations about cooperating with Obama, but he sees the use of gas in Syria as a dangerous prelude to its possible use in Russia, a totally unacceptable prospect for any Russian leader. In this circumstance, Putin is ready for limited cooperation with Obama on Syria, a place of traditional Russian influence and power for many decades.

Second, the Boston marathon tragedy. Here Putin’s problems with Islamist radicalism have now directly affected his relations with the United States. Cooperation seemed appropriate, and he provided a good deal of help to the CIA and the FBI, even approving of the visit of FBI director Robert Mueller. Both Putin and Obama obviously see the Boston tragedy as another reason to cooperate on a broader front.

There are other reasons, too. Putin was worried enough about Israel’s recent air attacks against missile shipments near Damascus that he took the unusual step (for him) of telephoning Israeli prime minister Benyamin Netanyahu to urge caution and restraint, even to agree to meet with him in the near future. He also knew that the United States had recently moved hundreds of special forces into northern Jordan, not only to help train Jordanian troops but also to prepare for quick entry, if ordered, into Syria’s bloody civil war, which at the moment seems no closer to any solution.

Perhaps most important, Putin is aware that the pressure on Obama to intervene militarily in Syria has now reached the boiling point. The usually tight-lipped White House has been deliberately leaking stories that all make one point: Obama does not want to intervene militarily, but since chemical weapons have been used in Syria, though in a limited way, and since he warned, more than once, that this “red line” must not be crossed, and since he has boldly proclaimed that he is not one to “bluff,” Obama has painted himself into a corner. He must act to retain his dignity and to keep his word.

During his recent visit, Kerry’s implied message to Moscow was not only an urgent appeal to cooperate on Syria and arrange a new international conference; it was also a warning that if this conference does not produce a positive outcome, meaning the gentle but necessary ouster of Assad and the formation of a new government, Obama would have to dramatically up the ante and inject American military power into the Syrian civil war, introducing a wildly new and unpredictable element.

It is for Obama a huge diplomatic gamble, a last gasp before action. If it fails, then, despite his obvious hesitation, he may feel obliged to order the American military into another war in the Middle East. For Putin, it is also a gamble, but not nearly of equal dimension.

Marvin Kalb, a guest scholar at Brookings, is author of The Road to War: Presidential Commitments Honored and Betrayed, which is to be published by Brookings in early June.