Overton window
Joseph Overton explained why libertarian think tanks exist by creating a chart of different political ideas that it’s possible to have with a straight line from “most government, least freedom” to “least government, most freedom” and said that the ideas that politicians can get away with supporting are in the middle of it but sometimes where that is changes. For example,  Prohibition is something that people once supported while being in the mainstream but then society changed so that no politician could get away with supporting prohibition because society moved towards more freedom and less government. Overton also said that society could move in the direction of less freedom and more government. Overton said libertarian think tanks existed to move society to the point where more libertarian ideas were more mainstream and statism was seen as more radical. After Overton died, his think tank, the Mackinac Centre, started to call that idea, the Overton Window.