There is an increasing number of districts that favor just a single party. Several accounts focus on gerrymandering but we need to look beyond just the redistricting problem to understand why this issue is happening. This article by Alan I. Abramowitz is published by Center for Politics. Here is an excerpt:

Congress is dysfunctional, and many political observers believe that gerrymandering is a significant reason why. Gerrymandering — the drawing of U.S. House (and state legislative) district lines by partisan actors to benefit themselves and their party — is seen as contributing to a growing proportion of seats that are safe for one party, and therefore to declining competition in House elections. As a result, this argument goes, members of the House are increasingly concerned with their own party’s primary voters rather than the broader electorate and have little incentive to work with colleagues from the opposing party.

In this article, I examine the impact of redistricting on the competitiveness of House elections over the past 5 decades. I show that, based on presidential voting patterns, the proportion of districts that strongly favor one party or the other has doubled while the proportion that are closely divided has fallen by 50%. However, this long-term decline in the competitiveness of House districts is not primarily a result of redistricting. In fact, the same trend is evident in U.S. states and counties, whose boundaries do not change over time the way congressional districts do.

Despite the growing proportion of districts that strongly favor one party based on presidential voting, the actual margins of House elections have changed very little over the past 50 years, and partisan turnover has fallen only slightly, if at all. The explanation for these contradictory trends is that the personal advantage of incumbency has declined dramatically since the 1980s: The ability of House incumbents to attract votes across party lines and thereby insulate themselves from competition is now much more limited than it was in the 1970s and 1980s.

Read the full story here. Also see related Democracy Chronicles articles like those on Redistricting, Election History, or even seen our section on American Democracy.