When Barack Obama was elected into office three years ago, a popular sentiment began to take America by hold: that America had matured into a post-racial society. But not everyone agrees with that thought. Randall Kennedy argues in his new book, “The Persistence of the Color Line: Racial Politics and the Obama Presidency,” that race is anything but in the past. Kennedy is a Harvard Law School professor. He joins us from our partner WGBH in Boston.