 leaders of the 32 nations in the NATO alliance and partner countries, including Ukraine and Japan. The first event is this evening, a commemoration ceremony at the Mellon Auditorium, the location where the NATO treaty was formally signed in 1949. Thursday, he holds an event with Ukraine's President Zelensky and nearly two dozen allies and partners who, like the U.S., have signed security agreements with Ukraine. That evening, the president will hold a rare solo press conference, something he hasn't done since last November. Karen Travers, ABC News, the White House.