Interactive graphic by Christopher Ingraham. Data from Voteview.com. Original concept by Brian Resnick, Brian McGill and Ella Krivitchenko of the National Journal.
Similar to the party unity graph, you can plot legislators' dw-nominate scores, which indicate ideological positions -- increasingly positive values indicate more conservative leanings, while negative values indicate more liberal leanings.
Again, our era is unique in its ideological spread -- there is a full 1.069-point gap in the difference between mean Democratic and Republican scores, the largest on record. The 1940s stand out as a period of relatively small ideological difference, with gaps of less than 0.5 points.
Across several periods there is overlap at the tail ends of Republican and Democratic parties, which the most li