MOSCOW — President Vladimir V. Putin has been many things to President Obama: a partner at times, an irritant more often, the host of the elusive Edward J. Snowden and “the bored kid in the back of the classroom” who offered so little on the administration’s foreign policy goals that Mr. Obama canceled plans to hold a summit meeting in Moscow last week.

Yet suddenly Mr. Putin has eclipsed Mr. Obama as the world leader driving the agenda in the Syria crisis. He is offering a potential, if still highly uncertain, alternative to what he has vocally criticized as America’s militarism and reasserted Russian interests in a region where it had been marginalized since the collapse of the Soviet Union.

Although circumstances could shift yet again, Mr. Putin appears to have achieved several objectives, largely at Washington’s expense. He has handed a diplomatic lifeline to his longtime ally in Syria, President Bashar al-Assad, who not long ago appeared at risk of losing power and who President Obama twice said must step down. He has stopped Mr. Obama from going around the United Nations Security Council, where Russia holds a veto, to assert American priorities unilaterally.

More generally, Russia has at least for now made itself indispensable in containing the conflict in Syria, which Mr. Putin has argued could ignite Islamic unrest around the region, even as far as Russia’s own restive Muslim regions, if it is mismanaged. He has boxed Mr. Obama into treating Moscow as an essential partner for much of the next year, if Pentagon estimates of the time it will take to secure Syria’s chemical weapons stockpile are accurate.