Scott Alexander examines which US political party has become more extreme faster, concluding Democrats have moved further left on policy since 1994, while results vary for other aspects of extremism.
Longer summary
Scott Alexander analyzes the question of which political party in the US has become more extreme faster, breaking it down into four sub-questions. He concludes that Democrats have moved further left on policy positions since 1994 than Republicans have moved right, based on survey data and first principles. On divergence from ordinary Americans, he calls it a tie. Regarding ideological purity, Republicans show more polarization in Congress, but it's unclear for average voters. Scott avoids declaring a winner on which party has become crazier in worldview and messaging. He argues the policy position change is most important, supporting the meme that Democrats have moved more extreme, while noting other interpretations could point to Republicans.
Shorter summary