The White House says it still believes a diplomatic solution to the dispute with Russia is possible. Obama spoke with Putin for more than an hour Thursday, outlining a potential resolution that would include Russia pulling its forces back in Crimea and direct talks between the Kremlin and Ukraine.
But the fast-moving developments in Crimea may mean that the ultimate question facing Obama is not what the U.S. can do to stop Russia from taking control of Crimea, but what kind of relationship Washington can have with Moscow should that occur.
White House advisers insist the U.S. could not go back to a business as usual approach with Russia if Moscow were to annex Crimea or recognize its independence. But that may be seen as an empty threat to the Kremlin after the U.S., as well as Europe, did just that in 2008 after Russia recognized the independence of Abkhazia and South Ossetia, two breakaway territories of Georgia. Russia also continues to keep military forces in both territories.
Privately, U.S. officials say Russia is running a similar playbook as it seeks to increase its influence in Crimea. And regional experts say Putin also appears to have a larger goal: influencing central government lawmakers in the Ukrainian capital of Kiev as they prepare for elections later this spring.
"It says to the Ukrainians, 'Don't mess with me or I'll slice off a finger,'" said Matthew Rojansky, a Russia analyst at the Woodrow Wilson International Center for Scholars.
The months-long political crisis in Ukraine bubbled over late last month when protesters in Kiev ousted pro-Russian President Viktor Yanukovych. Amid the chaos, thousands of Russian forces took control of Crimea, a strategically important outpost in the Black Sea where Moscow has a military base.
The outcome of the Crimea referendum is not guaranteed, but there are clear indications the region will choose to side with Russia. About 60 percent of Crimea's population already identifies itself as Russian. And Crimea's 100-seat parliament voted unanimously Thursday in favor of joining Russia.