The debate is over: Gerrymandering gives GOP a chance to retain House

This is a season of gerrymandering. A federal court in Texas will soon rule on whether the state discriminated against minorities when it adopted its current congressional map. The Supreme Court will hear the biggest case of all in October: a challenge to Wisconsin’s partisan gerrymander with the potential to curb partisan gerrymandering nationwide.

But before the courts weigh in, it’s time to end the last debate over partisan gerrymandering. That’s the one that unfolded after the 2012 election, when Democrats won the House popular vote but fell 17 seats short of taking the chamber. It caused a classic feud between “data” and the conventional wisdom, with data journalists and political scientists contending that gerrymandering wasn’t responsible for Republican control of the House.

Now, the electoral context has changed, and the old debate is moot. Heading into the 2018 midterms, data and conventional wisdom agree: Gerrymandering is a big reason the GOP has a real chance to retain control of the House, even if the Democrats score a clear win.

Most of the political-science-based estimates suggested that gerrymandering cost the Democrats a net of 7 to 12 seats in 2012 (with a few estimates coming in higher and lower).

That wouldn’t be enough to prove decisive in 2012, not with the Democrats falling 17 seats short. But in other contexts, that’s potentially a very significant number. If the party had come somewhat closer to retaking the House, most political scientists and data journalists would have probably conceded that partisan gerrymandering was at least plausibly responsible for the GOP’S margin of victory.

Similarly, the Democratic margin of victory in the House popular vote simply wasn’t very large: a single percentage point. The political scientists needed only to find that the alternative explanations for the Republican edge — incumbency and the

The Democrats routinely win 80-plus percent of the vote in big cities worth many congressional districts. There are very few places where the Republicans win 80-plus percent of the vote. The result is the remaining vote — and remaining districts — tilt Republican.

tendency for Democrats to “waste” votes in heavily Democratic cities — could account for that percentage point. Those who saw gerrymandering as the main cause of the GOP victory implicitly assumed that those alternative explanations added virtually nothing to the Republican edge.

There is little question that incumbency and geography help bias the House playing field against the Democrats. The incumbency advantage is perhaps the best-established effect in U.S. elections, and Republicans entered the 2012 election with many more seats than the Democrats. The Democratic geography disadvantage has been harder to clearly establish, but there is little doubt that it exists. The Democrats routinely win 80-plus percent of the vote in big cities worth many congressional districts. There are very few places where the Republicans win 80-plus percent of the vote in an area with enough people to form a congressional district. The result is the remaining vote — and remaining districts — tilt Republican.

Minnesota has emerged as a compelling example. The map was drawn by a judicial panel appointed by the state Supreme Court after the Democratic governor rejected plans by the Republican-led Legislature. Hillary Clinton won the state but took only three of the state’s eight congressional districts. And Donald Trump won the median congressional district by 8 points, meaning Democrats have to win in districts that favored Trump by a clear margin to claim a majority of the state’s congressional districts.

What makes Minnesota so compelling is that the state’s political geography in presidential elections has shifted to become more like the rest of the country. It used to be the rare state where Democrats were competitive or even victorious among rural voters, but in 2016 it exhibited the more typical pattern of big Democratic strength in the cities and Republican strength in the countryside. As the political geography became more typical, so did the Democratic disadvantage.

It’s hard to quantify the effect of political geography on the Democratic disadvantage nationwide, much as it’s hard to quantify the effect of gerrymandering. What’s clear, though, is that both effects are real, and it’s hard to argue that incumbency and geography couldn’t have made the difference in the Democrats’ failure to take the House in 2012.

But it’s not 2012 anymore. If the political environment doesn’t change significantly before next November, Democrats could be poised for a sweeping victory in the midterm elections — one far greater than their victory in 2012. In that sort of political environment, the Republicans will need every advantage they can claim to hold the House. Partisan gerrymandering would be essential to their path to victory.

Nate Cohn covers elections, polling and demographics for The New York Times.