The fate of the current Wisconsin Assembly district map, precision-engineered to maintain a Republican majority in the face of anything short of a major Democratic wave election, is in the hands of the Supreme Court, which could announce a decision in Gill v. Whitford any day.
One theory of gerrymandering is that the practice isn’t much of a problem, because the power of a gerrymandered map “decays” with time — a map that suits a party in 2010 may, due to shifting demographics, be reasonably fair a few years later.
How’s the Wisconsin gerrymander doing in 2018? We just had a statewide election in which Rebecca Dallet, the more liberal candidate, beat her conservative rival by 12 points, an unusually large margin for a Wisconsin statewide race.
The invaluable J. Miles Coleman broke the race down by Assembly district:
Dallet won in 58% of seats while getting 56% of the vote. That sounds fair, but in fact a candidate who wins by 12 points is typically going to win in more seats than that. (That’s why the courts are right to say proportional representation isn’t a reasonable expectation!)
Here’s the breakdown by Assembly district, shown a little bigger:
Dallet won by 2 points or less in 8 of the Assembly districts. So, as a rough estimate, if she’d gotten 2% of the vote less, and won 54-46 instead of 56-44, you might guess she’d have won 49 out of 99 seats. That’s consistent with the analysis of Herschlag, Ravier, and Mattingly conducted last year, which estimates that under current maps Democrats would need an 8-12 point statewide lead in order to win half the Assembly seats. (Figure 5 in the linked paper.)
I don’t think the gerrymander is decaying very much. I think it’s robust enough to make GOP legislative control very likely through 2020, at which point it can be updated to last another ten years, and so on and so on. This isn’t the same kind of softcore gerrymandering the Supreme Court allowed to stand in 1986, and I hope the 2018 Supreme Court decides to do something about it.