In the aftermath of the Paris attacks, two pictures sent a powerful message about how international politics is changing. One was of United States President Barack Obama hunched in discussion in a hotel lobby with Russian President Vladimir Putin. The frosty body language of their previous meeting at the United Nations had given way to something more businesslike. The US and Russian presidents almost looked like colleagues. The second picture, artfully released by the defence ministry in Moscow, was of a Russian bomb being loaded on a plane in Syria with the words "That's for Paris" scrawled on the side.
Together, the two images highlighted an interesting possibility. Might Russia and the West begin to bury their differences by making common cause in the war against the Islamic State in Iraq and Syria (ISIS)? The idea horrifies many Russia analysts in the West and presents enormous complications. Nonetheless, it is worth a try for a number of reasons.
First, foreign policy is about setting priorities - and after Paris, with the threat of further attacks to come, the defeat of ISIS is rightly the top Western priority. Second, there have been some modest but important signs that Russia is backing off in Ukraine. The ceasefire in the east of the country held throughout the autumn. There has been a flare-up of fighting in recent days but not all of it has been driven by the Russians. Finally, neither the West nor Russia has a monopoly of wisdom on the Syrian conflict. Finding a middle ground between the entrenched positions of Moscow and Washington could help end the conflict.
The Putin government's fiercest Western critics argue that Russia's annexation of Crimea and military engagement in eastern Ukraine were such fundamental breaches of international law that Russia ultimately presents a bigger menace to the world order than ISIS. But that is a hard argument to make at the moment to the European and American public , who can see that the extremists pose a direct and immediate security threat to the major cities of the West in a way that Russia does not.
The Russia hawks point out that the war unleashed in Ukraine has cost thousands of lives. Russia's military build-up continues. The Russian government has embraced a highly nationalistic and anti-Western worldview.
Also, Mr Putin has a record of turning aggression on and off as political circumstances dictate. Taking the pressure off now, they argue, might encourage future Crimeas.
These arguments cannot be waved away. So any move towards a rapprochement with Russia has to be gradual and conditional. The European Union has correctly decided not to ease sanctions on Russia, for now. But if the ceasefire in Ukraine is restored and holds, and Russia is constructive on Syria, then some alleviation of sanctions becomes much more likely in the first half of next year.
Those who oppose an attempt at rapprochement with Russia also argue that Mr Putin's real motive in Syria has less to do with the defeat of ISIS than with re-establishing Russian power in the Middle East and handing the US a symbolic defeat. They point out that most early Russian air strikes were aimed at the "moderate" Syrian opposition, rather than ISIS. They add that Russia's aim of keeping President Bashar al-Assad in power will ultimately empower the extremists - because hatred of Mr Assad is their biggest recruiting sergeant.
These points also have some force. But they still do not invalidate the case for trying to work with Moscow on Syria. The Russian government has now accepted that ISIS was behind the attack on a civilian airliner in Sinai that killed hundreds of Russian citizens. Perhaps, as a result, in recent days many more of its air strikes have been directed at ISIS.
The fate of Mr Assad remains a significant dividing line between the Western powers and Russia. The big regional powers are even more bitterly divided over this issue, with Iran backing Mr Assad to the hilt and the Saudis and Turks demanding that he leave office.
The Western powers and their allies are right that Mr Assad's brutality has served as a rallying cry for Sunni Arabs and helped the extremist cause. But the Russian response also has merit. Their argument is that any vacuum after the fall of Mr Assad is likely to be filled by some mixture of violent chaos and extremism - circumstances that could be designed for ISIS to thrive in. Conditions on the ground in Syria and the experiences of Iraq and Libya make this Russian analysis hard to refute. Without really acknowledging it, the US has, in any case, moved gradually towards the Russian position, dropping its insistence on the immediate departure of Mr Assad. The very real threat that both Russia and the Western powers face from ISIS may now concentrate minds enough to force them to bridge their remaining differences over the fate of Mr Assad.
After the Paris and Sinai attacks, the undoubted strategic rivalry in the Middle East between Russia and the West should be trumped by a shared strategic and moral interest in the defeat of ISIS and the achievement of peace in Syria.
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