As Swing Districts Dwindle, Can a Divided House Stand? By NATE SILVER

In 1992, there were 103 members of the House of Representatives elected from what might be called swing districts: those in which the margin in the presidential race was within five percentage points of the national result. But based on an analysis of this year’s presidential returns, I estimate that there are only 35 such Congressional districts remaining, barely a third of the total 20 years ago.

Instead, the number of landslide districts — those in which the presidential vote margin deviated by at least 20 percentage points from the national result — has roughly doubled. In 1992, there were 123 such districts (65 of them strongly Democratic and 58 strongly Republican). Today, there are 242 of them (of these, 117 favor Democrats and 125 Republicans).

So why is compromise so hard in the House? Some commentators, especially liberals, attribute it to what they say is the irrationality of Republican members of Congress.

But the answer could be this instead: individual members of Congress are responding fairly rationally to their incentives.Most members of the House now come from hyperpartisan districts where they face essentially no threat of losing their seat to the other party. Instead, primary challenges, especially for Republicans, may be the more serious risk.

The New York Times | Five Thirty Eight
As Swing Districts Dwindle, Can a Divided House Stand?
Nate Silver