KYIV, Ukraine—Ukrainian President Volodymyr Zelensky pushed back on a U.S. proposal to recognize Russia’s control of Crimea as part of a cease-fire agreement, throwing into doubt President Trump’s efforts to bring a quick end to the war. “Ukraine will not legally recognize the occupation of Crimea,” Zelensky said at a press conference here on Tuesday. “There’s nothing to talk about here. This is against our constitution.” Zelensky’s dismissal upends Trump’s latest gambit to halt the war in Ukraine—now in its fourth year—and casts new uncertainty on the future of the relationship between Kyiv and Washington, which Trump has made conditional...