Administration officials privately acknowledge there is little chance Putin will give up Crimea, a strategically important peninsula that has long housed a Russian military base. Instead, the most pressing U.S. concerns are now cooling tensions in Crimea, where both Ukraine and Russia have troops, and preventing Putin from pushing into areas of eastern Ukraine that have similarly pro-Russian populations.
Secretary of State John Kerry said any further Russian incursion into eastern Ukraine would be a "major breach." But he declined to give specifics on how the U.S. would respond.
Even as the U.S. and Europe talk tough, there are practical concerns on both sides of the Atlantic that are likely to factor into future decisions about punishing Russia.
European nations, including powerful Germany, have deep economic ties to Russia and fear Putin could retaliate financially if the EU ordered tougher sanctions. The U.S. is also dependent on Russia keeping open supply routes the Pentagon is using to withdraw from Afghanistan, and relies on Putin's cooperation on an agreement to strip Syria of its chemical weapons stockpiles.
And perhaps most pressing for Obama is Russia's partnership in tense international negotiations with Iran, which are aimed at blunting the Islamic republic's nuclear program.
The Russians aren't interested in easing those concerns. A top Russian diplomat told the Interfax news agency Wednesday that Moscow may revise its stance in the nuclear talks in response to actions taken by the U.S. and Europe.
EDITOR'S NOTE: Julie Pace has covered the White House for The Associated Press since 2009. Follow her at http://twitter.com/jpaceDC