Overton window: A term that refers to the acceptable range of public discourse, with those venturing outside the window considered non-mainstream.

It is named for Joseph Overton, who developed the idea at Michigan’s Mackinac Center for Public Policy in the mid-1990s. Overton noticed that in some areas, only a narrow range of potential policies are seen as palatable.

“This ‘window’ of politically acceptable options is primarily defined not by what politicians prefer, but rather by what they believe they can support and still win re-election,” the center’s website says. “In general, then, the window shifts to include different policy options not when ideas change among politicians, but when ideas change in the society that elects them.”

Many pundits believe Donald Trump has jolted the Overton window far more than any presidential candidate in history. National Review’s David French argued that liberals previously had shifted it on gay marriage and transgender rights and were trying to do so on gun control.

“Then along came Donald Trump,” French wrote. “On key issues, he didn’t just move the Overton window, he smashed it, scattered the shards, and rolled over them with a steamroller. On issues like immigration, national security, and even the manner of political debate itself, there’s no window left. Registration of Muslims? On the table. Bans on Muslims entering the country? On the table. Mass deportation? On the table. Walling off our southern border at Mexico’s expense? On the table.”

On the liberal Rachel Maddow Blog, Steve Benen cited not just Trump’s stances, but the subsequent rightward posturing of other GOP candidates on immigration and the treatment of Muslims. “Watching the Overton window move with such incredible speed is exasperating,” he said.

But Vermont Sen. Bernie Sanders also is seen as helping to push the window in the opposite direction. Writing in Salon, Bob Cesca contended that “for the first time in 50 years, the Overton window appears to be slowly moving leftward. For this, Bernie ought to receive a significant share of the credit. Obviously, two terms of the Obama administration, helmed by arguably the most progressive chief executive since FDR, hasn’t hurt either. But the best indicator of this leftward voyage has been Hillary Clinton’s cleverly perceptive adaptation of Bernie’s positions.”

In a larger sense, social media has played a massive role in moving the window, said Clay Shirky, a New York University writer-in-residence who studies the Internet’s impact on society.

“The Overton window was imagined as a limit on public opinion, but in politics, it's the limit on what politicians will express in public,” Shirky wrote in a series of tweets last month. “Politically acceptable discourse is limited by supply, not demand. The public is hungry for more than politicians are willing to discuss.”

Social media is breaking the political 'Overton Window' -- the ability of elites to determine the outside edges of acceptable conversation. — Clay Shirky (@cshirky) February 18, 2016

The fact that people of all ideologies can invoke the Overton window undoubtedly sustains its continued popularity. Far-right provocateur Glenn Beck even wrote a 2010 political thriller with the title.

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Chuck McCutcheon writes his "Speaking Politics" blog exclusively for Politics Voices.

Interested in decoding what candidates are saying? Chuck McCutcheon and David Mark’s latest book, “Doubletalk: The Language, Code, and Jargon of a Presidential Election,” has just been released.