The Rising Incumbent Reelection Rate: What’s Gerrymandering Got to Do With It?

I’ve been thinking about reasons why Republicans have maintained control of the House. One story is gerrymandering, but according to this paper by John Friedman and Richard Holden, gerrymandering has been declining in its importance over the last half-century:

ABSTRACT: The probability that an incumbent in the United States House of Representatives is reelected has risen dramatically over the last half-century; it now stands at more than 98%. A number of authors and commentators claim that this rise is due to an increase in bipartisan gerrymandering in favor of incumbents. Using a regression discontinuity approach, we find evidence of the opposite effect. All else equal, changes in redistricting have reduced the probability of incumbent reelection over time. The timing of this effect is consistent with the hypothesis that legal constraints on gerrymandering, such as the Voting Rights Act, have become tighter over time. Incumbent gerrymandering may well be a contributor to incumbent reelection rates, but it is less so than in the past.