The battle for Bakhmut in Ukraine's war-torn east has become one of the most brutal chapters of Russia's disastrous invasion of its neighbor, as Ukrainian defenders burrowed into lines of fortified positions and mud-swamped trenches fight off waves of Russian assault units picking their way across the shell-scarred landscape. The grinding assault on the city and its surrounding area is a rallying point for Russia's military bloggers and propagandists, and a showcase of the capabilities of the Wagner Group and leader Yevgeny Prigozhin, one oligarch ally of President Vladimir Putin whose profile has increased dramatically since February 24. Prigozhin and...