A peace proposal by the Trump administration that includes recognizing Russian authority over Crimea shocked Ukrainian officials, who say they will not accept any formal surrender of the peninsula, even though they expect to concede the territory to the Kremlin, at least temporarily. Giving up the land that was illegally annexed by Russia in 2014 is also politically and legally impossible, according to experts. It would require a change to the Ukrainian constitution and a nationwide vote, and it could be considered treason. Lawmakers and the public are firmly opposed to the idea. “It doesn’t mean anything,” said Oleksandr Merezkho,...