The latest crisis about whether or not chemical weapons were deployed by the Syrian government is following a well-established script. The United States has concluded that the perpetrator was likely the government of Bashar al-Assad, while Russia wants to wait until a United Nations inspection process is completed—but has already strongly hinted that it blames any chemical weapons use on opposition forces who it believes seized such weapons from the government's arsenal.
Moscow is urging the international community to let an inspection process continue—something that could take weeks to come up with any definitive result. Any further delay is politically unfeasible for an Obama administration coming under tremendous pressure, both from domestic political forces as well as from allies in Europe and the Middle East, to make good on the president’s "red line" declaration.
In theory, the Syrian government has accepted the necessity for such a mission, but this will most likely play out in the same way as previous attempts to verify claims about atrocities during the two-year long civil war with a welter of claims being made.
Russia is prepared to continue to use its veto power to block the United States from seeking authorization for any sort of military action—and Moscow is likely, if no definitive assignment of guilt can be made, to continue to blame the rebels rather than Assad's forces, and so not sign off on any American plan to punish Damascus. Thus, unless Moscow decides to accept that there is incontestable evidence that Assad is responsible, the current stalemate will continue. America’s out will be to use NATO to bomb Syria.
The deterioration of U.S.-Russia relations since 2011 pretty much eliminates any possibility of a joint, multilateral operation to secure dangerous stockpiles. Nor, given Vladimir Putin's deep conviction that Russia was misled about the U.S. intent when Washington sought a no-fly zone for Libya on the grounds of creating safe havens for refugees, will Moscow see any U.S. proposal to take action in Syria as anything but cover for pushing for regime change. If Washington wants to act more forcefully in Syria, it will have to do so without the imprimatur of the UN Security Council. It is not surprising, therefore, that there are reports that the Obama administration is carefully studying the precedents set during the 1999 NATO intervention in Yugoslavia, an operation which also proceeded without the blessing of the United Nations.
Just as in 1999, in the short term, should Washington act against Moscow's preferences, there is very little Russia will do to directly oppose American action. Syria, after all, has no mutual-defense treaty with the Russian Federation which would obligate Moscow to treat an attack on Syria as an attack on Russia itself. Russia would, of course, raise all sorts of procedural objections at the United Nations and raise a full-throated rhetorical defense of Syria, but would, as happened during the Kosovo war, do nothing to directly become involved itself. In that sense, the Obama administration probably does not need to factor in the risk of a direct U.S.-Russian clash over Syria—although the accidental bombing of the Chinese embassy in Belgrade during the NATO campaign is a reminder that exquisite care needs to be taken by U.S. military planners not to select any Syrian targets which run the risk of killing Russian civilians or advisors, which could have very negative, if unintended, consequences.