Ambassador William B. Taylor Jr. looked out over the front lines of Ukraine’s long war with Russian-backed separatists last July, taking in a damaged bridge and then farther in the distance, an “armed and hostile” enemy.

Taylor had taken the job of acting U.S. ambassador to Ukraine reluctantly, he said in congressional testimony Tuesday. His decision came only after assurances from Secretary of State Mike Pompeo in late May that President Trump was committed to helping Kyiv hold off forces, armed and funded by Moscow, that had besieged the country for nearly five years.