Overton slider
A politician or
media personality who continuously discusses extremists and extreme positions about public policy or cultural values so as to help slide a metaphorical "window" of acceptance over views what were once considered radical and far outside the mainstream. By often illustrating or focusing discussion on the extreme and radical exceptions and outliers, the previously unacceptable extremes will appear less extreme, and
soon come to be seen as a broadly held public view. And once this occurs, it can be voiced,
debated, accepted, and generally framed or enacted as a serious premise or rationale for a policy or behavior.