The front line in Ukraine changed little in the winter. Russia aimed to capture the entirety of the Donbas, but it only inched forward. Ukraine has made minimal gains in its counteroffensive. Dense Russian minefields and fortifications have made every attack extremely costly. Despite nine months of bloody fighting, less than 500 square miles of territory have changed hands since the start of the year. A prolonged stalemate could weaken Western support for Ukraine. Both sides started the year with lofty ambitions: Russia wanted to capture the eastern Donbas region, while Ukraine aimed to split Russian forces with an attack...