… The most widespread measure today is the one devised in the 1980s by political scientists Keith Poole and Howard Rosenthal, also known as Nominate. It maps members of Congress on a scale from left to right, based purely on their voting records. …
Congress is more polarized, according to Poole-Rosenthal, than it has been since the Civil War — which was the ultimate in polarization. … Part of what’s expanded polarization is the decline in representation by Democrats and Republicans who are more closely aligned with the other party — for instance, the conservative Democrats who once ruled the South. There is essentially no political overlap today between the most conservative Democrat and most liberal Republican. [cont.]
Carl Bialik, Wall Street Journal