March 23, 2022 6:12 PM EDT

Joe Biden had his hands full when he walked out the White House to start his four-day swing through Europe. Two cell phones were stacked together in one hand; a pair of his signature aviator sunglasses in the other. Over the thumping rotors of the waiting Marine One helicopter, a reporter asked Biden if he’s concerned about Russia using chemical weapons in Ukraine. “I think it’s a real threat,” Biden said, turning toward the spinning blades of the chopper and putting the glasses on.

The stakes are high for Biden’s trip. There are growing concerns inside the White House that Russia may escalate the war and cause massive civilian casualties in Kyiv or in the coastal city of Mariupol, which Russia has been shelling for weeks. The U.S. has pushed back against requests for North Atlantic Treaty Organization (NATO) countries to enforce a no-fly zone in Ukraine over worries that such direct combat could escalate into a broader war. But experts warn that a Russian escalation inside Ukraine could change that calculus for Western allies.

In the meetings in Europe on March 24 and 25, Biden will discuss Moscow’s potential use of chemical or biological weapons in Ukraine, how countries should respond to possible Russian cyber attacks, and how to deal with recent Russian rhetoric on nuclear weapons. He’s attending an emergency summit at NATO headquarters in Belgium and meeting with leaders of G7 countries and the European Union. Before returning to the U.S., Biden will visit President Andrzej Duda in Warsaw, Poland, on the eastern edge of the NATO alliance. Poland, which shares a border with Ukraine and Russia’s ally Belarus, has borne the shockwaves of Russia’s month-long war, taking in 3 million refugees and becoming the main pathway of weapons moving through to bolster Ukrainian defenses.

On the trip, Biden will also be trying to get allies to make sure financial punishments they’ve already put in place continue to pinch the Russian economy. The sanctions on Russian industry and financial transactions won’t mean much if Russia finds ways around them. Biden wants to see European allies tasking investigators and prosecutors with robust sanctions enforcement actions. “What we would like to hear is that the resolve and unity we’ve seen for the past month will endure for as long as it takes,” Biden’s National Security Adviser Jake Sullivan told reporters on March 23 aboard Air Force One on the way to Belgium.

But while Biden has largely kept NATO allies unified in their response so far, this trip will test the group’s resolve. There are disagreements among the U.S. and its allies on the extent of the current sanctions against Russia and the next steps. Finding ways to reduce Europe’s dependence on Russian oil and gas has been the subject of “intense back and forth” over the past fews days, Sullivan said, and is another “substantial topic of conversation” for Biden on the trip.

Biden banned U.S. purchases of Russian oil and gas on March 8. Germany and other European countries that rely more heavily on Russian energy imports have largely kept Russian fuel flowing. The Biden White House thinks Europe can do more to wean itself off from Russian energy. The U.S. wants Germany, for example, to go further in cutting off Russian energy purchases. White House officials have considered closing the U.S. banking system to electronic transfers paying for Russian energy but won’t take that harsh step without agreement from allies whose domestic energy supply is reliant on Russian gas and oil.

Germany, for its part, is looking for ways that the U.S. and other allies could ease the impact on the German economy if there are further reductions in the purchase of Russian energy. The U.S. has surged delivery of liquified natural gas to Europe in recent weeks, but European leaders want more assistance for investing in alternatives to Russian supplies. European countries also want to share the expense and effort of resettling refugees fleeing Ukraine. More than 10 million people have fled Ukraine in the fighting, and Europe is looking to the U.S. and other allies for ways to share the cost and impact of such a rapid mass migration.

Looming over Biden’s meetings is the question of how far China will go to prop up Russian President Vladimir Putin’s war in Ukraine and how allies should respond. So far, the White House has not seen evidence of China providing weapons or ammunition to Russia to help with the invasion, Sullivan said. But there’s increasing concern that China could take financial steps to blunt the longer-term impact of sanctions on the economy in Russia, a close trading partner. Biden wants to talk to allies to ensure “there isn’t systematic sanctions busting,” Sullivan said. “I don’t want to use the microphone to threaten, I just want to say this is something we are vigilant about.”

Putin’s aggression on NATO’s doorstep in Ukraine has clarified the alliance’s mission to protect Europe from invasion. Now, Biden wants to see NATO allies follow through on their commitments to boost military spending and deployment of troops and equipment in Eastern Europe. Military commanders from NATO countries are looking at what size troop deployments are needed over the next several months to protect Europe’s borders with Russia.

Given that Poland’s border with Ukraine is being used to resupply weapons from European countries to Ukrainian forces, Poland is one NATO ally currently in Russia’s crosshairs. Biden’s visit to the country at the end of his trip carries powerful symbolic weight for reaffirming the U.S. commitment to NATO and to Poland, says Steven Durlauf, a professor at University of Chicago Harris School of Public Policy. “They’re on the firing line; If Russia goes crazy and actually crosses a NATO border, it’s going to be theirs,” he says. Biden clasping hands with Poland’s president in Warsaw at this moment, “is largely symbolic,” Durlauf adds, “but this is the time when symbols carry weight.”

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