Politicians rarely lead opinion; they pick from ideas the public already accepts

Joseph Overton of the Mackinac Center for Public Policy described a 'window' of policies voters see as acceptable at a given time. Ideas outside it are politically unthinkable however good or bad they are, so politicians mostly choose from inside. The window moves as campaigners, events and public debate shift what seems reasonable. The term, coined by a colleague after Overton's death, is now used across the political spectrum.

— Mackinac Center for Public Policy, The Overton Window — Joseph Overton, 1990s