Casual reading of the Wikipedia page for George Moscone, the mayor of San Francisco who was murdered by demented former city supervisor Dan White, revealed the fascinating fact that he had appointed Jim Jones of the People's Temple to the city's Housing Authority. Jim Jones is of course more famous these days as the raving lunatic who orchestrated the Jonestown Massacre in Guyana, in which some 900 members of his cult were induced to poison themselves, but he seems to have spent much of the 1970s involving himself and his movement in progressive San Francisco politics. Jones seems to have been a fairly big player, someone that many liberal politicians were, for a time, anxious to have onside. One detail the Milk film omitted was the People Temple's involvement in some of Harvey Milk's election campaigns. It is perhaps easy to make too much of this - for a long time Jim Jones and the People's Temple must have seemed like just another bit of leftover 1960s counter-culture stuff, but it is still a fascinating detail.
Wikipedia page on the People's Temple in San Francisco (with lots of citations)