KYIV, Aug. 23 -- In the towns along Ukraine's northern border, where the memory of the 2022 encirclement of Chernihiv still shapes every threat assessment, the question has shifted from whether Russia can sustain its eastern offensive to whether Moscow is quietly preparing to reopen an entirely different front. President Volodymyr Zelensky gave that fear a sharper edge on Sunday.

Ukraine's president warned that Russia could redirect as many as 300,000 freshly mobilized troops toward the Chernihiv-Kyiv direction, the northern corridor left largely quiet since Russian forces withdrew in the spring of 2022, if Moscow achieves its objectives in Donetsk. "If he distributes 300,000 newly mobilized troops depending on what happens in the east o...