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.

On the air, the talk show host continuously featured guests talking about placing armed troops, and even land mines on the nation's borders, when his true position was a far less radical policy of better enforcement of immigration laws and policy. He was clearly another in a growing army of Overton sliders who have achieved a disturbing level of prominence in modern broadcasting.

Overton slider by shoqvalue July 21, 2010