If we were still a constitutional republic (practice, not theory), the political impact of social movements would largely be limited to the House of Representatives (popular support). Appointed senators would likely be more concerned with the legal, i.e. constitutional, aspect of a social movement. Between the two, the likely impact of a social movement SHOULD be limited to lower levels of government just like our founders intended.
Social movements arise from abuses at a particular level of government As a particular level of government grows larger and more powerful, the abuses at that level grow accordingly. The anti-war movement during the Vietnam War was fueled by the USA's unconstitutional entanglement in foreign affairs and forced conscription. Limit any abuses to the lowest level of government possible. Don't attempt to rectify abuses at the highest level of government.