Of all those, the candidate himself not least among them, who have commented upon the unlikeliness of Barack Obama?s run for president, its novelty and defiance of the norm, the rapper DMX appears to have maintained a uniquely pristine state of incredulity. ?His name is Barack?!? said DMX recently, in an interview with XXL Magazine. Yes, the interviewer assured him: Barack Obama. “Barack?!” Barack. “What the is a Barack?! Barack Obama. Where he from, Africa? . . . You can’t be serious. Barack Obama. Get the outta here.” One quotes these remarks less to marvel at the solipsism of a rap superstar than to note that hip-hop and politics have always been uneasy bedfellows. For every “conscious” or politically engaged rapper, there have been 50 others whose estrangement from the political process has acquired the density of an ideology. But here comes Marcus Reeves with Somebody Scream! — a coherent and clear-headed account of hip-hop culture in which its evolution is related at every turn to the prevailing reality of racial politics in America. That 1995 saw the Million Man March as well as the release of the fatherless Tupac Shakur’s Me Against the World was not, Reeves shows us, an idle simultaneity. The beating of Rodney King was prophesied in the music of NWA, and the killing of James Byrd answered in the roar of the aforementioned DMX. The controversy surrounding Public Enemy in the late 1980s, writes Reeves, “helped expose a vacuum of black leadership within black America, so much so that African Americans would mistake a rap group . . . for real political leadership.” Given the potency of the music, it was an easy mistake to make.