U.S. President Joe Biden flies to Europe on Wednesday for an emergency NATO summit on Ukraine, where invading Russian troops are stalled, cities are under bombardment and the besieged port of Mariupol is in flames. Four weeks into a war that has driven a quarter of Ukraine’s 44 million people from their homes, Russia has failed to capture a single major Ukrainian city, while Western sanctions have ostracised it from the world economy. 

After failing in what Western countries say was an attempt to seize Kyiv swiftly and depose the government, Russian forces have taken heavy losses, are frozen in place for at least a week on most fronts and face supply problems and fierce resistance. They have turned to siege tactics and bombardment of cities, causing massive destruction and many civilian deaths. Moscow says its aim is to disarm its neighbour, and its “special military operation” is going to plan. It denies targeting civilians.