Despite their bitter face-off from the United Nations General Assembly podium, President Obama and Russian President Vladimir Putin are likely to be uneasy collaborators, rather than adversaries, in the growing fight against Islamic State in Syria and Iraq.
Obama and Putin disagree bitterly over the future of Syrian President Bashar Assad, Russia's most important ally in the Middle East and the immediate beneficiary of Moscow's deepening political and military involvement in the region.
Obama on Tuesday repeated his call to oust Assad, whom the White House considers the chief instigator of a conflict that has left more than 200,000 people dead, spawned Islamic State's extremist army and sparked an international refugee crisis.
Defeating Islamic State "requires, I believe, a new leader" in Syria, Obama said at a U.N. conference on countering violent extremism, a hesitation perhaps meant to acknowledge that no moderate alternative to Assad has emerged from the horrors of a 41/2-year-old civil war.
U.S. officials have signaled their willingness to accept Assad's rule for now, given that his departure could lead to a total collapse of Syria and open the gates of Damascus to the extremist Islamist groups battling to take power, including Islamic State and Al Nusra Front, an Al Qaeda affiliate.
Obama and Putin even disagree on what, if anything, they achieved in a 95-minute closed-door meeting Monday that focused mostly on Syria.
Putin told reporters before he left New York that while "disputes remain," he and Obama "now have an understanding" and are "thinking together on the creation of appropriate mechanisms," suggesting some form of coordination against a common foe.
"We have a lot in common," he said.
Putin clearly gave the impression that he was taking the initiative, and that Obama was dealing with him as an equal, an image the Russian leader seeks to foster back home.
The White House initially downplayed the import of the meeting, suggesting it gave Obama "clarity on [Russian] objectives" but little more.
The Pentagon announced Tuesday that Moscow and Washington will begin regular talks to share information about military flight paths and other maneuvers in Syria and Iraq to ensure U.S. and Russian planes don't inadvertently collide or fire at each other.
Secretary of State John F. Kerry said the two sides had agreed on "fundamental principles" about Syria's future.
Both leaders felt that Syria should remain whole, that Islamic State should be defeated and that they should promote a "managed transition" to a new government, Kerry said. They still disagree, he said, on what that new government should look like.
Russia this month deployed fighter jets, attack helicopters, tanks and naval forces to western Syria. The sudden escalation alarmed the White House and spurred fear that Moscow would throw its military might behind Assad.
Putin said in his speech Monday that Russia has categorically ruled out deploying ground troops in Syria.
U.S. officials aim to hold him to that pledge, warning that Russia would not want to slip again into a military quagmire, as the Soviets did in Afghanistan during the 1980s.
The Kremlin leader's deepening role had been widely touted in Russian media for weeks, yet his address to the General Assembly was met with fawning assessments by pro-Kremlin analysts Tuesday on the airwaves, social media and the blogosphere.
Under #PutinPeacemaker, journalists and commentators posted photos and cartoons on Twitter that variously depict Putin as a wrestler with Obama in a headlock, crowned by a halo amid children's fairy-tale figures and single-handedly outweighing the combined leaders of Germany, France and the United States on a seesaw.
"Thanks president #Putin for your amazing job, people all over the world are grateful!" declared one Twitter user under the handle @Russ-Warrior and illustrated by an image of the 19th century flag of Novorossiya, the now-Ukrainian territory coveted by pro-Russia separatists.
"Putin @ UNGA in short: US destabilized the world & created ISIS; EU tried secretly 2 cut off Ukraine from Russia. We should be allies again," reads another tweet from an apparent Kremlin booster, referring to Islamic State by an acronym.
"He tried to open the eyes of the world and explain what the shortsighted policy of the United States could lead to" in Syria, Russia-1 television reporter Olga Skabeyeva asserted in her broadcast from New York.
The Obama administration and its allies worry that Russia could expand its military buildup and take on not only Islamic State but also other rebel groups, including some supported by the West, to secure Assad's shaky hold on power.
Russia has yet to launch any military operations, unlike the nearly two dozen nations involved in the U.S.-led military campaign that has hammered Islamic State with more than 7,200 airstrikes since August 2014.
Robert Ford, the last U.S. ambassador to Syria, says it is easy to exaggerate how much effect the Russian buildup might have in the Syrian war.
"They have a relatively weak hand trying to shore up Assad, when he's losing a war of attrition," said Ford, now a fellow at the Middle East Institute in Washington. "They've tied themselves to a corpse."
Some analysts saw the two leaders' U.N. speeches as largely aimed at making them look tough to domestic and international audiences.
But others worry that Putin's course isn't predictable.
Cliff Kupchan, chairman of the Eurasia Group risk-assessment consulting firm and a longtime Russia specialist, said Putin could avoid "significant increased tensions" with Washington if Russia confines military operations to bombing Islamic State and helping Assad hold the territory he now controls.
But he warned that Putin's objectives could change if Russia's military effort bogs down and his public relations win at the U.N. turns into an embarrassment.
"If there are Russian casualties, will he leave or double down?" Kupchan asked. "His goals could change.... He wants to reinforce his image as an alpha male."
Richter reported from the United Nations and Williams from Moscow.