“Again, to illustrate this point, DW-NOMINATE suggests that Congress became much less polarized in the 1920s and 30s,”
Historically ignorant hogwash.
The 19th century Democrats were ‘conservative’ populists, and in the 20th century liberal populists took over the Democrats, but the southern Democrat wing remained until after the 1960s. As such, the democrats in 1930s had 2 wings, one liberal and one conservative.
The Republicans have moved right, by absorbing the rump Democrat conservative wing that the Democrats left.
As reagan put it, “I didnt leave the Democrat party, the Democrat party left me.”
The Congress wasnt less polarized, it was just the power of the left wasnt as great and division were regional not party based.
Now in the age of Obama the Democrats are more ideologically polarized than ever. Have they ever been this leftist as a party? No!
At the same time we have "industrial' alignments AND "agricultural" alignments.
A lesson ~ decades back Southern farmers could not raise corn as well as those in the Corn Belt. Today, thanks to modern fertilizers Southern farmers get yields that rival, and sometimes exceed, those found in the Corn Belt.
That fact, and Roundup, seed drills, and an incredible degree of mechanization, has given Southern Farmers their much sought after THIRD SEASON. It has also given Corn Belt Farmers a SECOND SEASON, and in some places, a THIRD SEASON.
That has allowed a vast reduction in the need for a large year round farm labor force ~ so those folks moved off the farm into town and industry. A newer foreign based "pulse' farm labor group has grown up to provide people those 2 or 3 times a year when they are needed (mostly at harvest). That process, in turn, has created some serious dilemmas for the Democrats and Republicans.