“Russia’s actions in Ukraine challenge [the] postwar order,” he said. That was not what the Russians wanted to hear from the president. Moscow’s U.N. ambassador, Vitaly Churkin, sank deep in his chair, and its foreign minister, Sergey Lavrov, looked on stony-faced. “Russia poured arms into Eastern Ukraine, fueling violent separatists and a conflict that has killed thousands,” Obama said. “When Ukraine started to reassert control over its territory, Russia gave up the pretense of merely supporting the separatists and moved troops across the border.” The president was not finished. “This is a vision of the world in which might makes...