Biden makes surprise visit to Ukraine nearly one year after Russia's invasion

In a sign of how sensitive the trip was, the White House had notified the Kremlin of Biden’s visit ahead of time, National Security Adviser Jake Sullivan said.

"We did so some hours before his departure for deconfliction purposes," he told reporters in a briefing. "Because of the sensitive nature of those communications I won't get into how they responded or what the precise nature of our message was.”

It is the first time in modern history that a U.S. president has entered a war zone where there is not an active American military presence. Ukrainian police and military had a strong presence and much of the central part of Kyiv was shut down, paralyzing traffic nearby.

Biden’s appearance in Ukraine is a strong statement that the U.S. stands with Zelenskyy despite growing pressure at home to downsize American aid.

“The first visit of the President of the United States to Ukraine in almost 15 years is the most important visit in the history of Ukrainian-American relations,” Zelenskyy posted on the social media site Telegram after the trip concluded.

Biden insisted that the U.S. will remain steadfast in its support of Ukraine.

"For all the disagreement we have in our Congress on some issues, there is significant agreement on support for Ukraine,” Biden said.

He announced an additional aid package worth $460 million, which will include more military equipment and weapons like anti-tank Javelin missiles.

Zelenskyy said that when Russia invaded, the U.S. was the first to call him in support.

Biden also recalled speaking to Zelenskyy — and the promise he made to help "rally the world" to Ukraine's cause.

“Russian planes were in the air and tanks were rolling across your border," Biden said. "You told me you could hear explosions in the background, I’ll never forget that. And the world was about to change. I remember it vividly."

The two leaders greeted each other with a sense of familiarity.

“Thank you for coming,” Zelenskyy said, according to a press pool report.

“More importantly, how are the children?” Biden said. He added, “It’s amazing to see you.”

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.

Biden also visited the U.S. embassy in Kyiv.

Former House Speaker Nancy Pelosi, D-Calif., said in a statement that the visit was a "powerful statement of America’s unshakeable support for the heroic people of Ukraine."

“On this Presidents’ Day, our President’s historic visit to Kyiv at this critical moment is a manifestation of America’s commitment to Democracy, in Ukraine and in the world," Pelosi said.

The trip came with risks. Other presidents have visited war zones. Barack Obama traveled to Afghanistan in 2014 and George W. Bush visited American troops in Iraq in 2003. As was the case with Biden, both traveled under strict secrecy.

White House officials had been adamant that Warsaw, Poland, would be Biden’s only stop. On Friday, a White House spokesman answered with a single word when asked if Biden intended to cross the border into neighboring Ukraine: “No.”

Now, the adversary is Russia. If Putin's military were to intentionally target Biden, or even inadvertently harm the president by way of an errant missile, the U.S. would be obligated to retaliate. That could potentially escalate a regional war into a direct conflict between two nuclear-armed countries.

Still, ahead of the trip, some analysts were hopeful that Poland would not be Biden's only stop. A trip to Ukraine "would be a powerful demonstration of support and signal a robust change in policy — a more forward-leaning and fulsome approach to Ukrainian support," said Alexander Vindman, former director of European affairs in the Donald Trump White House's National Security Council.