Regaining respectability: Mary Lou McDonald became president of Sinn Féin in 2018, following the retirement of Gerry Adams. Photo by Charles McQuillan/Getty Images Sinn Féin is in psychological turmoil. It wants to be seen as a contemporary party fit for office, shorn of its violent history and no longer inextricably tied to the IRA. But it does not want to betray its legacy, namely those who fought and died for the republican cause. The party’s president, 54-year-old Mary Lou McDonald, has come to symbolise this bipolarity: she is a slick, well-educated politician with a Dublin accent and the manners of...