Nine years after “A.D.I.D.A.S.” became his only substantial hit, Atlanta hip-hop fixture Killer Mike made a knockout album with an agenda that doesn’t even hint at pop crossover. Produced by El-P (whose own solo album of this year, Cancer 4 Cure, is worth hearing), R.A.P. Music is tough, lean and assured, the work of an artist who knows how hard he can strike. It also bubbles over with political fury: “Reagan” starts with a memory of the Iran-Contra scandal and its ripple effects on black America and goes on to indict all subsequent Presidents too.