The thick-necked union boss, who’s short on manners and long on tough talk and machismo, is in many ways an endangered American archetype. Amid rampant political correctness and professionalisation, they seem like anachronisms from a lost age; Sean O’Brien, president of the Teamsters, could be one of the last living specimens: his earthy ways evoke the Jimmy Hoffas and George Meanys of yore. In his speech at the Republican National Convention in the summer, O’Brien praised Donald...