A suggestion by the Trump administration’s top negotiator that an Ukraine peace deal would be based on talks conducted in Istanbul nearly three years ago has buoyed Russian officials and spooked Ukraine and its backers. To Kyiv, recent remarks by Steve Witkoff appeared to embrace the Kremlin’s key, and incorrect, talking point over the past three years: that Ukraine and Russia were about to strike a peace deal in Istanbul, and that Kyiv walked away from an agreement under pressure from Western politicians, such as then-British Prime Minister Boris Johnson. Russian President Vladimir Putin has repeatedly demanded that any future...