Few things in a democracy are more sacrosanct than the right to vote, and in his furious documentary “American Blackout,” Ian Inaba assembles compelling evidence to support his claim that African-Americans — who are traditionally more likely to vote Democratic — are being deliberately and systematically excluded from the political process. Interviewing Congressional leaders, journalists and regular voters, Mr. Inaba begins by addressing the Florida debacle of 2000, arguing that behind the exhaustive coverage of hanging chads and faulty voting machines lies an underreported and more complex story of black disenfranchisement. In a strong middle section, the movie examines the political troubles of Representative Cynthia McKinney, a vocal critic of the Bush administration, suggesting that her ouster in 2002 was engineered by Republican crossover voting. A particularly powerful segment shows how at least one of Ms. McKinney’s statements about the Sept. 11 attacks was edited by some commentators to appear infinitely less reasonable than the original.