Here's an excerpt from Buzzfeed:
The Overton Window, a theory named for the late think tank executive who developed it, postulates that there’s a finite range of policies or statements a politician can put forward, that are considered acceptable to the “mainstream” of that particular zeitgeist. If an idea is deemed politically and publicly acceptable, it is considered within the Window -- and, if it is not, proponents will seek to shift the window so that the statement no longer seems controversial.
Consider the effect of events like these on the Overton Window. In mainstreaming pronouncements of Obama’s otherness and displays of disrespect for his presidential legitimacy, federal and statewide elected officials steadily moved the border of publicly acceptable discourse crosswise. In so doing, they have served to normalize the kinds of messages – Obama isn’t working, Obama is in over his head, Obama is angry – that Romney has personally delivered for much of this campaign. After all, if questioning the president’s very legitimacy is now in bounds, Romney questioning his intelligence or work ethic hardly seems extraordinary in that context.
And it’s this same new climate that regularizes jokes that Obama is so inept he must rely on a teleprompter in order to speak, and which makes us almost immune to shock when a reporter barks at the president during a press conference in the Rose Garden.
Which brings us back to Romney’s remarks on Friday. Four years ago, describing Obama’s election as a risk was met with public disapproval. Today, questioning his very legitimacy has become a mainstream position pushed by some prominent elected officials in the Republican party.