There is always an urgency to put an end to war. But there is a growing urgency to bring an end to the war in Ukraine. That urgency was expressed in Ukrainian President Volodymyr Zelensky’s claim that the Trump administration had set a June deadline for negotiating an end to the war. Even NATO Secretary General Mark Rutte, a strong advocate for defending Ukraine, recently told Ukraine’s parliament that “getting to an agreement to end this terrible war will require difficult choices.” The urgency is also being felt in Russia, where Vladimir Putin’s patience with Donald Trump is stretching...

As peace in Ukraine struggles to be born after three-and-a-half years of war, necessity prompts each of the participants in different ways. For Ukraine to achieve its best possible outcome, it must find a diplomatic way to avoid outright military defeat. Russia, by contrast, does not feel compelled to end the war for military reasons, and, if it is to end it diplomatically, it must reach at least the key diplomatic goals it entered the war to achieve. Russian President Vladimir Putin would clearly prefer to end the war diplomatically, rather than militarily. Despite accusations that he has...