5) Media: There has been some debate as to whether the American electorate has become more polarized since the 1980s, but there is no debate as to whether the media has been, particularly with the proliferation of choices opened up by cable television in the 1980s, the internet in the 1990s, and the Fox News channel in the 2000s. Television programs that show incivility have been shown to have a negative impact on viewers' interest in political participation (See work by Dianna Mutz)
[we will soon have an academic white paper here, with links to research on the role of the media in fostering incivility, extremism, and political disengagement]