At their best, documentaries illuminate the world around us and can even result in policy changes, unjustly-imprisoned people being freed, and help spark political movements. With a heated presidential election around the corner, we revisited political documentaries from decades gone by, winnowing down a large group of contenders to a select group of 10. Some were so provocative their studio or TV backers avoided releasing them, while others were a hit out of the box. These documentaries tackle topics from voter suppression to a mock election in a Chinese elementary school. Several won Oscars; they all have enduring power.