Must-read by Christopher Ingraham, with great data from the Poole-Rosenthal numbers.

Political scientists have known for years that political polarization is largely a one-sided phenomenon: in recent decades the Republican Party has moved to the right much faster than Democrats have moved to the left. As Thomas Mann of the Brookings Institution has described it, “Republicans have become a radical insurgency—ideologically extreme, contemptuous of the inherited policy regime, scornful of compromise, unpersuaded by conventional understanding of facts, evidence, and science; and dismissive of the legitimacy of their political opposition.”

The data backing this claim up are pretty solid. The most widely-used measure of political polarization, a score of ideology based on votingdeveloped by Kenneth Poole and Howard Rosenthal, has shown that the Republicans in the Senate and especially the House have drifted away from the center far more rapidly than Democrats.