Volodymyr Zelensky of Ukraine had hoped to secure U.S. support in any cease-fire talks with Russia. Instead, his curdled relationship with President Trump was revealed in the Oval Office.

The upbraiding in the Oval Office came at a critical juncture in the war, with Ukraine striving to keep Russia at bay in battles of attrition in the country’s east and the Trump administration opening cease-fire talks directly with President Vladimir V. Putin of Russia.

Mr. Zelensky at no point backed away from what he has called Ukraine’s critical national interests, laying these out as a seat at the table in cease-fire talks; air defenses to protect Ukrainian cities and power plants; and U.S. military backup for a proposed, European-led peacekeeping force.

But it was unclear where Mr. Zelensky’s curdled relationship with Mr. Trump leaves Ukraine, which had relied heavily on American support over the last three years, and which had tried for weeks to broker a mineral rights deal that would satisfy the Trump administration.