As a Harvard historian, Serhii Plokhy comfortably analyzes timelines that span centuries. After finishing his latest book “The Russo-Ukrainian War” early this year, Plokhy wrote a new afterword at the end of August about the failure of Russia’s offensives and internal divisions illuminated by Wagner boss Yevgeniy Prigozhin’s abortive mutiny in June. Since summer, however, his outlook has grown more somber, with concerns around the stalling Ukrainian counteroffensive, intensifying Russian attacks, and delay of further military aid to Ukraine.