Last October, when Kevin McCarthy was ousted as speaker of the house, one Republican of the eight who voted against him stood out as the odd bedfellow of the group: a junior representative from South Carolina named Nancy Mace. The seven other Republicans, all men, were far-right rabble-rousers, loudmouths for whom grousing about the “establishment” rather than working with it was always the right political move. They were used to attracting and capitalizing on press attention. Yet in the days that followed McCarthy’s ouster, Mace outshone them all, showing up for work in a shirt with a red A on...