The world just got a hint of a tantalizing but possibly even more dangerous future without Russian President Vladimir Putin. The Western stakes in the Ukraine war rose significantly as a result. A mutinous weekend that saw mercenary chief Yevgeny Prigozhin flagrantly mock the Kremlin before aborting his march on Moscow evoked Russia’s blood-soaked history of revolutions and coups. Meanwhile, efforts by the White House and its foreign allies to find out exactly what was happening underlined the volatile nature of a war that could rewrite the map of Europe and modern history. Ultimately, a civil war that seemed about...