The clandestine nature of the trip points to the dangers of America's commander-in-chief visiting Ukraine amid continuing bombardment, as Russia continued firing missiles into the country hoping to break an impasse as the war enters its second year. Air raid sirens sounded while Biden was on the ground.

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.