I think that as Gamewell suggested, the last period of major activism in America took place between the 1950's and the 1970s where you had the Civil Rights, Women's Liberation, Anti-war and Environmental Movements which was followed by a period of generally progressive legislation and fairly liberal fiscal and social policy lasting until the 1980s with a gradual shifting to the right, beginning with less liberal fiscal policy but eventually including increasingly conservative legislation, the loosening of restrictions on financial institutions and more conservative social policy characterized by wars on crime and drugs, increased policing, abortion debate etc. and a re-emergence of activism developing in the new millennium i.e. civil rights (black, LGBTQ, women), environmental and anti-war. If this is a cyclical process and the past is a predictor of the future, then a shift to the left will occur.