Northern democrats and party polarization in the US House

Over the last 25 years, there has been a steady increase in party voting in the U.S. House, with much of this increase attributed to changes in the South. We argue that changes in the North are also important. Democrats now win a higher percentage of elections in the North, and a larger percentage of the congressional party comes from the North. Northern Democrats became steadily more liberal in the 1980s and 1990s, which increased the liberal record of the entire party. We examine two factors in the rise in liberal voting in the North. First, Democrats now win more seats in urban, lower-income, nonwhite districts that tend to generate liberal voting records. Second, there has been an increase in the number of districts that tend to produce liberal-voting Democrats. Together, these changes have resulted. in more liberal Democratic Party voting and greater polarization between the par-ties.