political polarization

This chart above comes from a June 23, 2005, New York Times article "One Nation, Divisible" , points out that in 1955 33% of house members and 39% of senators were centrists while it was 8 and 9% in 2004. They attributes polarization to political redistricting, which makes seat safe for representatives with more extreme views which extended to the Senate as House members moved up.
See a summary in the section on Political polarization in the home page here.

A February 29, 2012, article "After Many Tough Choices, the Choice to Quit" about Main Senator, Olympia Snowe's decision not to run again, talks about the difficulties of being a centrist. It points out,

"Ben Nelson of Nebraska, the senator often considered the most conservative Democrat, and Ms. Snowe, seen as the most liberal Republican, will both be gone next year, as will Senator Joseph I. Lieberman of Connecticut, an independent who left a Democratic Party that would not tolerate his pro-Iraq war stand. They follow a parade of centrists out the Senate doors in recent years, including the Democrats Blanche Lincoln and Evan Bayh; a Republican-turned-Democrat, Arlen Specter; and two Republicans-turned-independents, James M. Jeffords and Mr. Chafee."

As anger over the state of politics increases apathy, "only the most rabid partisans vote," so political strategists steer campaigns to issues that turn them on, said former Republican governor of New Jersey and Environmental Protection Agency administrator, Christie Whitman, who supports abortion rights. For Republicans, those are often social issues like abortion, gay marriage and contraception. But the rise of a new strain of fiscal conservatism has also led to moralistic portrayals of votes on spending and the debt limit. And when issues are framed around morality, compromise becomes very difficult.

"You can't compromise with someone who's amoral," she said.

There is an indication that the general public is becoming more polarized.

Several reasons have ben proposed.

The Echo Chamber Effect:
Around 2004, Cass Sunstein, a professor at the University of Chicago Law School, started referring to the effect of associating with people we agree with as the echo chamber effect.

In military circles, this process is called "incestuous amplification." Among psychologists, it is known as "group polarization." In a nutshell: Like-minded people, talking only with one another, usually end up believing a more extreme version of what they thought before they started to talk.
See: NPR "On the Media", Feb., 6, 2004

More choices in media, Fox and MSNBC instead of just ABC, NBC and CBS, and a multitude of Internet based media choices, blogs, facebook friends, etc. contributes even more to this process.

Books - Articles:
Book: Going to Extremes: How Like Minds Unite and Divide, by Cass Sunstein, 2009
Radio: On The Media (NPR): Transcript of "The Echo Chamber Revisited" (June 17, 2011)
Article: How a High Choice Media Environment Leads to Greater Selectivity, Fragmentation and Polarization, by Rebecca Chalif, 2010

Links:
Are the Media Biased?

last updated 4 Mar 2012