1. A political theory invented by arch-conservative Joseph Overton, VP of the anti-tax Mackinac Center for Public Policy in Midland, Michigan. (Overton died in 2003 when his ultra-light airplane crashed.)
2. The name of a poorly-written novel by right-wing talk show host Glen Beck. Published in early 2010, the book is a cautionary tale about leftist radicals taking over the government through incremental change.
In theory, the Overton Window represents the boundaries of "acceptable" public policy and discourse -- what a politician can support without seeming too "extreme." Opposing forces try to broaden this window (or shift it to one side) to make formerly "radical" ideas seem more "mainstream."
Overton's theory has a decidedly pro-business, anti-regulation slant. Something is either "more free" or "less free" in his view. He never mentions "more just" or "more fair" or "more practical." In fact, the entire theory tailor made for paranoid people and right-wing lunatics who think Obama is a totalitarian Marxist dictator bent on world domination.
RWW has an extensive story about Paul Nehlen, an unapologetic nazi who is running again in an attempt to unseat Paul Ryan. Nehlen is intent on shoving the Overton Window as far right as possible, to ‘sanitize’ and normalise white supremacy and nationalism.