The ADA and ACU, like many other interest groups, annually choose votes important to their supporters and then rate members of Congress on how often they support the organization's positions. Between 1992 and 2000, the American Conservative Union's average rating for all members of the House increased from 43 to 51. Over the same period, the Americans for Democratic Action's average House rating fell from 56 to 42. Forty-three state delegations became more conservative from 1992 to 2000, the analysis shows. The GNS findings are counter to the theme that centrists have been a rising force in Congress.
Political scientists have varied explanations for the increased polarization.
There is a need to raise money, and you go to the respective power constituencies of both parties. There are not a lot of liberals at the Chamber of Commerce, and there are not a lot of conservatives in the comparable groups on the left. Even so, there are centrist coalitions. But some say it's not like it was. Sen. Joseph Biden, D-Del., said that Democrats have been forced to the left in order to oppose GOP entrenchment on the right.