Written as the keynote for the 2018 Canadian Association for American Studies (CAAS) conference, this article draws on the author's personal experience, half-century of historical research, and American art and fiction to examine American mainstreams and alternatives from the boundaries and borderlands of American social relationships and discourses. In the contexts of the Trump administration's alleged "fake news" and "alternative facts," it probes who defines the mainstream, who decides what stories are mainstream (or canonical), whose accounts more "authentic" or "alternative" or just plain lies. Adding marginalized people and movements to history destabilizes "mainstream" histories distorted by skewed sources, silenced stories, and an assumed historical "mainstream" or "consensus." Marginalized actors push the boundaries of national histories that do not easily accommodate multiple actors or perspectives. "Mainstream" histories of the nation that focus on public politics and powerful actors can make most people appear insignificant and erase the daily acts and grass-roots movements that change the historical mainstream. From unexamined margins, people start or catalyze social change with daily acts that begin to transform social relationships. Changes born in marginalized borderlands can become mainstream truths.