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Why the Democratic wave may be bigger because of gerrymandering

I’ve been saying for a while that I think the Democrats will probably retake the House in 2018. More recently the probability seems to be getting higher and higher if you look at the generic ballot.

But I noticed something on Twitter and made an observation which I think perhaps I should put here: the conscious Republican gerrymandering after 2010 opens the possibility for greater Democratic gains because of tail risk. I was prompted to this comment after seeing a distribution of likely outcomes of the November 2018 election. The shape of the likely number of Republican/Democratic representatives wasn’t Gaussian. Rather, there was a much longer Democratic tail to the distribution. I hypothesized that this was the outcome of massive Democratic gains if the wave was high enough, and gerrymandering districts begin to overtop and flip.

The logic is pretty straightforward. Republican gerrymandering involves packing Democrats into some districts and dividing others between very Republican districts. The packing decreases the proportions of Democrats in some Republican districts. But the dilution of Democrats across very Republican districts, leaving somewhat less Republican, but still reliably Republican, districts, is where my point comes in.

If the national generic ballot swing toward Democrats is large enough, then some safe Republican seats come into play. Distribution of Democrats across these districts in a normal year does not entail anything more than a trivial shift in probabilities. But in a wave election, the standard operating procedure might not hold. If the Democratic votes were in a single district, then the Republican districts that remained would be more robust to a wave. As it is, removing these safe Democratic districts and distributing them across Republican districts made these districts a little less robust to a wave.

3 thoughts on “Why the Democratic wave may be bigger because of gerrymandering

  1. The other part of it is that gerrymandered districts decay over time because the underlying demographic assumptions don’t hold. But I’m more skeptical of any wave because of geographic sorting, which I believe is increasing.

  2. Are thicker tails (on a distribution of additonal seats won for each %age vote change) an inevitable result of gerrymandering — defined here as cracking and packing?

    Put another way, the objective function for a gerrymanderer in any given state is to max the number of Republican seats given the partisan distribution. But a secondary objective should be to “wave proof” the gerrymander by maximizing the percentage democratic vote required for them to win a majority of seats. Is there a trade off between these two objectives (max seats, max wave point) for a given partisan distribution, and how does the trade off change as the partisan distribution changes (e.g, state becomes more Republican)?

    There is a pretty deep statistical literature on gerrymandering, but all i found was from the perspective of Luke, none from the Vader point of view. I found one paper from 1998 that might answer this question directly, but I don’t feel like paying $43.

  3. Another part of a wave election is candidate recruiting. Quality candidates don’t run in races that are perceived to be unwinnable. Sometimes no one runs on the ticket of the party with an uphill battle, and other times the candidate is a sacrificial lamb with little funding and a weak resume and commitment to the race. If there is a perception that a race is winnable due to an anticipated wave (even if the polls supporting that perception aren’t actually very predictive), strong candidates will run, will commit more effort to the races, and will be better funded, putting what had looked like a fairly safe seat in play and exposing the weaknesses of a candidate in a safe seat.

    Also, the available funds for defense of incumbents beyond what they raise themselves from their own district and personal contacts is not unlimited, and if credible candidate run in more races, those funds are spread more thinly. So, running a credible candidate in a race with a low chance of success can still undermine other less secure candidates in a wave election.

    Contrawise, candidates in marginal seats will sometimes choose to retire in the face of a wave election turning an otherwise difficult race against an incumbent into a much more winnable open seat.

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