WASHINGTON — President Joe Biden’s decision to make a risky wartime visit to Kyiv took root after a similarly clandestine mission just two months ago — when Ukrainian President Volodymyr Zelenskyy came to Washington and addressed a joint meeting of Congress, according to two sources familiar with the matter.

Senior members of Biden’s national security team who had helped arrange that travel at the end of last year were heartened — and pleasantly surprised — by how powerful and positive the reaction to Zelenskyy’s trip seemed to be among the American people, the sources, who like others in this story were granted anonymity to discuss internal planning, said. It was Zelenskyy’s first travel outside Ukraine since the start of the war.

Hoping to sustain momentum for efforts to keep the fragile Western alliance together in support of Ukraine, those officials began discussions about potentially using the anniversary of Russia’s invasion to make a similarly bold gesture.

Publicly, that planning would play out in the trip officials formally announced 10 days ago — that Biden would be making a second trip to Poland, Ukraine’s neighbor, to meet with its president and other NATO allies who have most to lose from any weakening in western resolve.

But privately, among a small universe of senior officials, the thinking was that this might be the moment to realize a long-held hope among some officials for an even more potent demonstration of U.S. solidarity: having Biden visit Ukraine. 

“Discussions about possibly going have been underway for months, and really accelerated in recent weeks,” said one senior administration official.

Officials across the government had long made clear that it was nearly impossible to guarantee the safety of the commander-in-chief heading into a warzone in which the U.S. is not an active partner.

Other NATO and G7 leaders, senior members of Congress, the secretaries of Defense and State had all made the long, secretive journey to Kyiv. First Lady Jill Biden made a surprise Mother’s Day visit to western Ukraine, spending two hours in the border town of Uzhhorod to meet First Lady Olena Zelenska. 

But the level of security needed for the president of the United States had long been deemed incompatible with the task. Even until the end, discussions around security measures were “intense,” as another official put it. It even included a call to Russian officials hours before Biden’s departure for “deconfliction” purposes, National Security Adviser Jake Sullivan would later tell reporters. 

“[It] required a security, operational, and logistical effort from professionals across the U.S. government to take what was an inherently risky undertaking and make it a manageable level of risk,” Sullivan acknowledged to reporters after Biden departed Kyiv Monday afternoon local time. “But, of course, there was still risk and is still risk in an endeavor like this.”

Biden spent about five hours in the capital, meeting with Zelenskyy and other Ukrainian officials. The two leaders visited St. Michael’s Golden-Domed Monastery and then walked to the nearby Wall of Remembrance, which honors those who have died in the war.

Sullivan and his deputy, Jon Finer, said that while planning involved officials from across the government, it was a very close hold among each agency involved. 

During a White House press briefing on Friday, National Security Council spokesperson John Kirby flatly denied that Biden would detour to Ukraine on his Poland trip. 

Typically, it would be Sullivan briefing reporters ahead of a Biden foreign trip, but he did not do so this time so as not to be in the position of misleading reporters, according to two sources familiar with the matter.

As planning reached late stages, aides to Vice President Kamala Harris were told that her itinerary around the Munich Security Conference needed to be trimmed to ensure that she returned to U.S. soil by Saturday night. They were not given a reason, only that it was “non negotiable,” according another administration officials.

On Sunday, the White House released a public schedule for Biden that had him scheduled to depart for Poland late Monday — well after he had already quietly left Washington.

Instead, a handful of officials gathered at the White House before dawn, along with others at locations in Europe, to track his journey every step of the way, according to two officials.

Sullivan was among the limited number of staff traveled with Biden Monday; others who were due to travel with Biden to Poland will still travel, without Biden, as scheduled Monday night. 

White House officials did not immediately provide additional details of the precautions taken to minimize the security risks of the trip. But one obvious hurdle was how to provide security without committing U.S. air assets in the region.

Biden took a 10-hour train ride from the Polish border into Kyiv. A source familiar with the matter tells NBC News says while Biden could have gone to other locations inside Ukraine that would have been easier to access, he chose Kyiv to highlight that the capital is still standing after Ukraine’s forces proved to Russian President Vladimir Putin that the country would be more different to topple than anticipated.

For Jill Biden’s visit to Ukraine last May, military aircraft tracked her motorcade as it made its way from a Slovakian airport up to the border, but did not follow along as she drove across Ukraine’s border. The first lady’s trip was only made public as she prepared to cross back into Slovakia hours later.

When then-Vice President Joe Biden last traveled into a warzone, an April 2016 trip to Baghdad and Erbil, his arrival was disclosed after he had safely arrived in the Green Zone, with subsequent movements covered by the traveling press pool.

Biden noted that Monday’s was his eighth trip to Ukraine, and his first words after stepping off the train were, “It’s good to be back in Kyiv,” according to the press pool that made the journey with him.

Biden’s last visit to the country came in his final days as vice president.

This time, Biden “was very focused on making sure that he made the most of his time on the ground, which he knew was going to be limited,” Sullivan said.