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When a partisan gap becomes a chasm

The typical political conversation follows a predictable trajectory: the usual suspects argue that politics in Washington is broken because "both sides" have become more extreme, are beholden to their unyielding party bases, and are opposed to compromise. Folks like me try push back, arguing that this is wrong -- one party has been radicalized, the other hasn't -- leading the establishment to roll its eyes and dismiss my argument as overly partisan and ideological.

If only there was a way to quantify matters, removing opinions and subjectivity out of the equation. Wait, there already is such a way.

Political scientists Keith Poole and Howard Rosenthal periodically update their DW-NOMINATE scores, and yesterday, they published a new report reflecting the entirety of the 112th Congress. The data, as Dylan Matthews noted, is "the industry standard system for measuring how members of the House and Senate compare to each other ideologically."

And what did they find? The above image shows the ideological trajectory in the U.S. House since the last 1870s, and the blue line shows House Republicans reaching an extreme unseen since the dawn of the modern two-party system.

What about Democrats? They've been about the same since the mid-1990s.

The picture in the Senate is very similar.

The result isn't just a polarized Congress; it's the most polarized House ever recorded, and the most polarized Senate since the post-Civil War Reconstruction era. It's not because "both sides" pander to their bases; it's because Republicans moved sharply to the right.

Poole and Rosenthal have more useful information in their report, including some additional charts. Be sure to share it with everyone who tells you "both parties" always deserve all of the blame.