The East-West showdown over Russia's annexation of Crimea, which challenged the post-Cold War compact in Europe, will dominate each stop of Obama's tour to Poland, the Group of Seven summit in Belgium and France for 70th anniversary commemorations of the D-Day landings.
On the World War II battlefields in France, there will be several potentially awkward personal encounters between Obama and Russian President Vladimir Putin, whom he has spent months trying to isolate over Ukraine. Washington insists there will be no formal summit between the two leaders.
Obama will also meet leaders still coming to terms with European Union elections that saw voters in several member states lash out at the bloc's political establishment by backing radical euro-skeptic parties.
The political earthquake could threaten one of Obama's top foreign policy priorities, the negotiation of a massive Trans-Atlantic Trade and Investment Pact (TTIP).
Obama also wants a strong, unified Europe to maintain the threat of tougher sanctions if necessary on Moscow over Ukraine and to reduce its dependence on Russian energy.
The Ukraine crisis and Putin's trashing of a "reset" relationship with Washington -- one of the diplomatic prizes of Obama's presidency -- has emboldened the president's critics at home and disrupted a foreign policy based on ending US wars and rebalancing power to the Asia Pacific region.
Obama will use the trip to renew US security assurances to eastern European NATO members and seek to reinvigorate NATO -- an organization suddenly newly relevant after years searching for a role after the demise of the Soviet Union.
- Powerful moment -
In Warsaw, Obama will take part in the 25th anniversary celebrations of Poland's first post-communist elections, which have taken on extra poignancy amid the worst showdown between the Kremlin and the West since the end of the Cold War.
"It's a very powerful moment to... look back at the history of how Polish democracy was won," said Obama's Deputy National Security Adviser Ben Rhodes.
The president will also "look at the current moment and the need for the United States and Europe to stand together on behalf of the security of Eastern Europe, and to stand in support of democratic values and all of those who would reach for democratic values as we've seen so powerfully in Ukraine these last several months," Rhodes said.
In Warsaw, Obama will have his first meeting with Ukraine's president-elect Petro Poroshenko, days before his inauguration, and underline US support for his effort to lead out of a political and economic crisis which saw the overthrow of president Viktor Yanukovych in February.
The former leader was toppled amid during protests sparked when he declined to sign an association agreement with the European Union, under pressure from Moscow.
Obama says Ukrainians must have the chance to decide their country's own future -- even as their nation's unity is torn by worsening clashes between pro-Moscow separatists and Kiev government forces in eastern regions.
"We don't know how the situation will play out and there will remain grave challenges ahead," Obama said in a major foreign policy address on Wednesday.
"But standing with our allies on behalf of international order working with international institutions, has given a chance for the Ukrainian people to choose their future without us firing a shot."
Poland's ambassador to Washington Ryszard Schnepf said that his own country's journey from the gray uniformity of decades behind the Soviet Iron Curtain into an era of pluralism and economic vitality should give Ukraine hope.
"At the beginning of the 1990s, Poland was in the same situation economically as Ukraine is now," he said.
"The Polish path is not only a perfect example for surrounding countries -- but first of all for Ukraine."
Obama will lead talks with former Warsaw Pact nations now in NATO, including Bulgaria, Croatia (part of the old Yugoslavia), the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovakia.
He arrives in Warsaw on Tuesday to hold talks with President Bronislaw Komorowski and Prime Minister Donald Tusk. He will move on to the G7 summit in Brussels on Wednesday, and have a one-on-one meeting with British Prime Minister David Cameron.
The US leader will dine with French President Francois Hollande in Paris on Thursday, before heading the next day to Normandy for ceremonies on Omaha and Sword beaches and a lunch with foreign leaders -- including Putin.