Dave Wasserman, the Cook Political Report writer who likes redistricting so much he made it his Twitter handle, offered a bold challenge. First he drew a GOP-friendly gerrymander of Wisconsin, a state whose underlying partisanship is 50-50.

Then he promised a $7,000 prize to any reader who drew an equally gerrymandered map favoring Democrats. He probably should have offered more money because it’s literally impossible — at least with the software Wasserman was using.

Twitter challenge: Wisconsin has a partisanship score (PVI) of EVEN. Below, I've drawn a GOP gerrymander where 6/8 districts have a score of R+7 or higher.



I will personally award $7,000 to the first follower who draws a Dem gerrymander where 6/8 districts are D+7 or higher. pic.twitter.com/h0dJ922FAE — Dave Wasserman (@Redistrict) March 27, 2018

Wassermann was working with Dave’s Redistricting App, an invaluable (albeit tricky-to-use) web app that lets you draw your own congressional maps with accurate data about population levels and partisan lean of every precinct in America.

And the problem for Democrats is that the electoral precincts out of which the maps are made are themselves “gerrymandered,” such that it is far more common to find that there’s a precinct that’s 85 percent or more Democratic than one with such a heavy GOP tilt.

That matters because the way to create a partisan gerrymander is to group together a whole bunch of heavily Democratic precincts in order to create a single district that serves as a vote sink while giving the GOP smaller, but still nearly insurmountable, edges in the others.

Since the GOP-tilting precincts don’t tilt as severely, the GOP vote sinks you’d craft to make a Democratic gerrymander aren’t nearly as effective. To draw six districts that have a D+7 lean in Wisconsin, you need the two remaining districts to have an R+21 lean. But there aren’t enough individual precincts that are R+21 or more to make that work. However, there are plenty of D+21 precincts so you can draw the 6-2 GOP gerrymander.

This is in part a limitation of the software, but the fact that the same situation arises in essentially every state illustrates that some profound — and not necessarily benign — dynamics are at work that give the GOP a systematic edge at the gerrymandering game.

Segregation begets gerrymandering

Real-life state legislatures are, of course, allowed to redraw or break up voting precincts if they want to. At a certain point, gerrymandering the precincts themselves becomes inconvenient for voters, but it works in a pinch.

Still, you’d find this same dynamic if you relied on census tracts instead of voting precincts.

And you’d find it for basically the same reason. America’s white majority tends to vote Republican while its nonwhite minority backs the Democrats. But the parties are electorally competitive because the GOP tilt of the white population is much less severe than the Democratic tilt of the nonwhite population — Trump won 57 percent of whites while Clinton got 74 percent of nonwhites, according to the 2016 exit polls.

If the racial mix of the country was flat across the entire landscape, that would be irrelevant. But, of course, it isn’t flat. America’s social geography is characterized by enormous amounts of neighborhood-level racial segregation. This translates into partisan politics and means that essentially any form of district drawing that is based on geography will be heavily influenced by the way black and Latino neighborhoods (and Indian reservations) serve as Democratic vote sinks.

It’s common among redistricting analysts to refer to this sort of thing as a “natural” aspect of American geography, though obviously there’s nothing especially natural about the dynamics that replicate neighborhood-level segregation over and over again across the country. That means Republicans inherently have the upper hand in the gerrymandering game.

Fair districting helps Democrats

Republicans did very well in the 2010 midterms, so the preponderance of gerrymandering in current congressional maps reflects GOP priorities. That’s why these days you hear more about the evils of gerrymandering from Democrats and why Democrats are more enthusiastic than Republicans about the idea of trying to get courts to rule partisan gerrymanders unconstitutional.

But that’s essentially a question of happenstance.

Democrats draw favorable maps for themselves when they can, and in the future may have more state legislatures under their control to draw maps for. As recently as 2002, a Democratic-drawn map for Texas gave Democrats a majority of its US House delegation long after national realignment had turned it into a red state.

The geographical reality, however, is that this is a game Republicans are going to play more effectively on a systematic basis. So rules requiring districts to fairly represent the overall voting behavior of the state would, in the long run, be better for Democrats — unless they stop being the preferred party of racial minorities or residential segregation vanishes as a phenomenon.