The deepening dispute between East and West is expected to dominate his visit to Europe, which begins Monday in the Netherlands. The four-country trip was long-planned, but now provides the U.S. and Europe a well-timed chance to present a united front against Russian President Vladimir Putin.
But behind the scenes, Obama will be gauging how far the still economically shaky European Union is willing to go in punishing Russia, one of its largest trading partners. He'll also be confronted with other European frustrations with the U.S. that are bubbling just below the surface.
Some European officials, chief among them German Chancellor Angela Merkel, are still smarting over revelations of National Security Agency spying on the continent. There's also lingering resentment among EU leaders over what it sees as Obama's snubbing of the alliance.
"There's an anger there, there's a frustration there," said Heather Conley, a Europe expert at the Center for Strategic and International Studies. She added that while the Ukraine crisis may "mute" some of Europe's irritation with Obama, "it doesn't solve it."
In the Netherlands, Obama will join world leaders at the Nuclear Security Summit and head a hastily arranged meeting of the Group of Seven - the U.S., Britain, Canada, France, Germany, Italy and Japan.
The latter meeting will focus on boosting financial support for Ukraine's fledgling government, while also serving as a symbol of the West's efforts to isolate Moscow. Russia often joins the G-7 nations for Group of Eight meetings, including a summit Putin is supposed to host this summer. Those plans are now in doubt.
Russia is participating in the nuclear summit, but Putin will not attend. He's sending Foreign Minister Sergey Lavrov to The Hague.
Obama's focus on Ukraine will continue in Brussels, the headquarters for the EU and NATO. A later stop in Rome will feature a highly anticipated meeting with Pope Francis. Then it's on to Saudi Arabia for a fence-mending visit with the important Gulf ally.
Initial punishments from the U.S. and EU did little stop Russia from annexing the Crimean Peninsula from Ukraine. Western officials are now warily watching Russia build up its troop presence elsewhere along the former Soviet state's border.
Russian officials say those troops are simply participating in military exercises. But Obama's national security adviser, Susan Rice, said that given Russia's "past practice and the gap between what they have said and what they have done, we are watching it with skepticism."
The U.S. has warned that further Russian incursions could result in broader penalties targeting the Russian economy, including its robust energy sector. But administration officials acknowledge that American sanctions wouldn't have the same kind of bite as European penalties, given Europe's deeper economic ties with Russia.
That puts Obama in the position of seeking cooperation from the sometimes unwieldy EU, the 28-country bloc that has often bristled at what its leaders see as snubs by the American president.
The president has skipped over Brussels on all eight of his previous trips to Europe as president. He ended the practice of holding U.S-EU summits annually, preferring to hold meetings instead with individual European leaders. On the rare occasions when he has attended EU summits, the meetings have been brief and yielded little of consequence.
"They know the president can't stand sitting in these meetings," Conley said of EU leaders. "They got that message very clearly."
The NSA spying disclosures have strained Obama's relations with Europe, particularly with Merkel, the leader with whom he had perhaps the closest relationship. Last year's explosive leaks from NSA contractor Edward Snowden included a revelation that the U.S. was monitoring Merkel's cellphone.
Former State Department official Jeremy Shapiro said that while anger over the NSA persists, Europe's leaders are unlikely to get let that matter bleed into discussions over Ukraine.
"Ukraine is too serious an issue for them." said Shapiro, now a fellow at the Brookings Institution. "Russia is too serious an issue for them. And the need to work with the United States is too serious an issue to complicate it with this type of thing."
The crisis in Ukraine seems likely to overshadow what had been expected to be the most-attention grabbling stops of Obama's trip - meetings with Pope Francis at the Vatican and Saudi Arabia's King Abdullah in Riyadh.
Obama has praised the new pontiff and sees a connection with Francis' recent statements on income inequality, an issue the president is pushing at home.
Hot-button issues in the Middle East will dominate Obama's stop in Saudi Arabia, his second visit to the kingdom as president. During meetings with the king, Obama will seek to alleviate the Gulf nation's concerns over U.S. nuclear negotiations with Iran and the White House's tepid role in quelling the Syrian civil war.
Associated Press writer Jim Kuhnhenn contributed to this report.
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