Ukraine’s president donned a bullet-proof vest Sunday and made his first trip to Kharkiv since the Russian invasion began in February, and while there he axed a high-ranking security official. The decision to travel to the country’s second-largest city was a pointed and public reassertion of Ukrainian control over the city, while the firing underscored both the strategic importance of Kharkiv and President Zelensky’s uncompromising stance on job performance in a time of war.