"The idea of the Overton Window of using people on the political fringe to change the terms of acceptable debate, that`s an idea that`s been hugely influential in conservative politics since Joseph P. Overton thought it up, making radical ideas seem acceptable by advocating for the unthinkable."

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The idea of the Overton Window is that there`s a fairly narrow window of proposals in any particular policy area that people will take seriously that wouldn`t get you written off as a kook. The way to move or expand that window is to advocate super extreme positions which change the realm of what`s politically possible because after something super nuts has been . floated, thereafter, slightly less nuts positions will start to look acceptable and moderate by comparison.

— Rachel Maddow