Neither Donald J. Trump nor The Occupy Movement invented Populism. Both are recent examples of socio-political groups that draw their respective energy from mobilizing discontent. As such, Populism is essentially reactive (if not necessarily reactionary). "Populists" have a long lineage, and have assumed many forms, throughout American history.
James Foster of OSU-Cascades surveys the history and consequences of American Populism, and sheds light on the latest "outbreaks" of populist exasperation within this context.