Yevgeny Prigozhin, the combative boss of Russia’s Wagner private military group, relishes his role as an anti-establishment maverick, but signs are growing that the Moscow establishment now has him pinned down and gasping for breath. Prigozhin placed a bet on his mercenaries raising the Russian flag in the eastern Ukrainian city of Bakhmut, albeit at a considerable cost to the ranks of his force and probably to his own fortune. He spent heavily on recruiting as many as 40,000 prisoners to throw into the fight, but after months of grinding battle and staggering losses he is struggling to replenish Wagner’s...