Almost nobody doubts that come September, Richard Trumka will become the AFL-CIO's next president, replacing the retiring John Sweeney. Having occupied the labor federation's secretary-treasurer position for nearly 14 years, he's done everything his boss and the ideological faithful could ask of him. That's a major reason why he and his slate are running unopposed. But more than Sweeney, Trumka, a trained lawyer, has a palpably combative edge, much of it honed during his tenure as head of the United Mine Workers of America. His far Left populism was on display Thursday in his written denunciation of the "mob rule"...