"How the Media Frames Political Issues" by Scott London
In The Emergence of American Political Issues (1977) McCombs and Shaw state that the most important effect of the mass media is "its ability to mentally order and organize our world for us. In short, the mass media may not be successful in telling us what to think, but they are stunningly successful in telling us what to think about." The presidential observer Theodore White corroborates this conclusion in The Making of a President (1972):
The power of the press in America is a primordial one. It sets the agenda of public discussion; and this sweeping political power is unrestrained by any law. It determines what people will talk and think about - an authority that in other nations is reserved for tyrants, priests, parties and mandarins.
McCombs and Shaw also note that the media's tendency to structure voters' perceptions of political reality in effect constitutes a bias: "to a considerable degree the art of politics in a democracy is the art of determining which issue dimensions are of major interest to the public or can be made salient in order to win public support." http://www.scottlondon.com/reports/frames.html