President Volodymyr Zelensky of Ukraine was returning from the front line last week when he joined a pivotal call with President Trump. Hours earlier, Mr. Zelensky had visited soldiers defending Ukraine’s northeastern Sumy region against Russian ground assaults. Now, stopping in the small city of Romny, he listened on a secure line with other European leaders as Mr. Trump outlined Russia’s proposal to end the war. Seeing a chance to broker peace, Mr. Trump told those on the line that he would meet one on one with President Vladimir V. Putin of Russia to try to seal an agreement. It was a direct challenge to Ukraine’s core principles that territorial issues be addressed only after a cease-fire and that no deal be concluded without Kyiv.
