(CNN) Vice President Kamala Harris is jetting to Europe Wednesday for a trip that became more complicated after one of her hosts -- Poland -- caught the United States by surprise with a proposal to provide its Soviet-era fighter jets to Ukraine.
What seemed like a straightforward mission turned more fraught when the Polish foreign ministry announced it was prepared to deploy the jets to the US Air Force's Ramstein Air Base in Germany, which in theory could then be provided to Ukraine. Ukrainian President Volodymyr Zelensky has pleaded for more aircraft amid the Russian invasion. But that offer had not been discussed with the US before Poland announced it publicly, and Polish officials did not bring it up with Secretary of State Antony Blinken when he was recently in Poland, either.
It appeared designed to avoid the appearance of Poland directly arming Ukraine in its battle against Russia, but created a conundrum for the United States, which is also intent on avoiding direct conflict with Moscow.
The episode neatly illustrated the fragile NATO politics Harris will wade into when she arrives in Europe on a mission to reinforce Western unity in the face of Russian aggression. Eastern NATO members like Poland are concerned Russian President Vladimir Putin may have his eyes set on them next, and the US is working overtime to reassure them their security is paramount.
At the same time, the NATO alliance is striving to avoid becoming directly engaged in the Russia-Ukraine conflict, which has precluded steps like enforcing a no-fly zone over Ukraine. The option of providing Ukraine with Soviet-era jets was viewed as a potential alternative.
Harris will be tasked with smoothing over the situation as she arrives in Warsaw late Wednesday on a mission to reassure one of NATO's easternmost allies the United States remains committed to its security amid fresh worries about Russia's intentions. The trip is the second time in a month that Harris has been dispatched to Europe as the Biden administration seeks to rally international support behind its efforts to isolate and punish Russia for the war in Ukraine.
"We have been in dialogue with the Poles for some time about how best to provide variety of security assistance to Ukraine. And that's a dialogue that absolutely will continue up to and as part of the vice president's trip," a senior administration official said ahead of Harris' departure for Warsaw.
"This is a key priority for us and for all of our NATO allies," the official went on. "And so, we expect that we will continue talking about how to achieve this really important objective. A number of people have had a variety of ideas and we think all of them are worth discussing and that's what we're going to continue doing."
US officials have privately weighed sending aircraft to Ukraine but have repeatedly noted the difficult logistical challenges that doing so would entail.
Ahead of her departure Wednesday morning, there were intensive conversations within the administration about how to work with Poland to come to some sort of agreement that allows the jets to reach Ukraine.
Harris is traveling to Poland and Romania at a critical juncture for Europe, and for the Biden White House.
"The past couple of months have all been very much focused on what has tragically become a defining issue for the entire administration," a second senior administration official said.
Harris, for her part, has "really been immersed in this issue," the first official said, "working intensively on a daily basis on all of the issues that are related to the ongoing crisis resulting from the Russian invasion."
Officials said Harris would arrive in Europe with a three-part message: That the US stands by its NATO allies; that it will continue to support the Ukrainian people; and that Putin has made a mistake that will result in "resounding defeat" for Russia.
Harris plans to focus intensively on "next steps" with her interlocutors in Europe this week, the officials said, including on implementing sanctions, accommodating a large flow of refugees and developing plans to provide more military assistance to Ukraine.
Discussions will center on "how we move the ball forward," the second official said. "As proud as we are of what we've done together as an alliance so far, we are very conscious that there are many challenges ahead."
It's Harris' third trip to Europe in the last five months and comes only a few weeks after she traveled to the Munich Security Conference to deliver a message of resolve as Russia was massing troops on Ukraine's border.
On Thursday, Harris is scheduled to meet Polish President Andrzej Duda, a hard-right nationalist whose erosion of the country's judiciary has drawn statements of concern from the European Union. Amid the tensions with Russia, however, the Biden administration has kept Duda close and deployed thousands of additional troops to bases in Poland.
In Warsaw, Harris will also meet with refugees who have fled violence in Ukraine, as well as American diplomats who relocated to Poland from the US Embassy in Kyiv, which was closed.
She'll travel onward to Romania, where refugees fleeing bombardments in Ukraine have been arriving by the thousands. Like Poland, Romania is a NATO member where the US has deployed troops amid heightened tensions with Russia.
President Joe Biden is eager to demonstrate his commitment to security in Europe as the continent endures its first land invasion in nearly 70 years. The flow of people out of Ukraine, which reached 2 million this week, is the largest refugee crisis since World War II, the United Nations said.
"A number of these countries, including the ones she will be visiting, have welcomed hundreds of thousands of refugees from Ukraine," White House press secretary Jen Psaki said this week. "She'll also be talking about our ongoing range of options and assistance that we've been providing to the Ukrainian people."
Harris has emerged as his highest-ranking envoy to a continent suddenly facing questions over its stability and security. She traveled in February to the Munich Security Conference as Russia was massing its troops on Ukraine's borders, delivering an address that laid out the American position and meeting with European allies to confer over their response.
In Germany, she met the leaders of Lithuania, Estonia and Latvia, three other NATO members anxious about Putin's future ambitions. She also met NATO Secretary General Jens Stoltenberg. Last week Harris spoke with the Prime Ministers from Poland, Romania, Latvia, Lithuania and Estonia, part of a sustained effort by the administration to engage its NATO allies on the Eastern flank.
It has been an intensive introduction to wartime diplomacy for a vice president without heavy foreign policy experience. Her presence in Europe is a signal from the White House that it takes its NATO obligations seriously and that coordinating support for Ukraine is a key objective.
Harris' supporters also say it demonstrates Biden's trust in her to represent the United States in Europe at a critical juncture for the continent.
White House officials said they don't have plans for Biden himself to travel to Europe in the near-term. A presidential foreign trip requires a far more robust infrastructure and would be difficult to execute quickly. By comparison, the vice president's team has been given just over a week to prepare for her visit.
Harris has worked over the past year to burnish her foreign policy credentials, helped in part by assignments given to her by Biden that introduced her to foreign leaders and placed her at the center of critical global issues.
Her experience prior to becoming vice president focused mainly on domestic issues, including when she was California's attorney general and later when she was a US senator. But Biden has dispatched her abroad several times, and she has been relatively well received by leaders eager to make inroads with the new administration.
There have been some stumbles, including in Central America, where her message to migrants to "not come" to the United States was poorly received by immigration advocates. A fall trip to Paris went smoother, and Harris received an enthusiastic welcome at the Munich conference, which was a regular stop for Biden when he was in her role.