Today is the deadline for Pennsylvania Republicans to submit a new congressional district map for gubernatorial approval, following a ruling from the state Supreme Court that the current districts are an unconstitutional partisan gerrymander that deprives the state's residents of participating in free and equal elections.
The practice of gerrymandering has come under increased scrutiny in recent years. In most states, the redistricting process is controlled by whichever party is in control at the statehouse at the time of redistricting. This creates a tremendous incentive for members of that party to draw district boundaries that benefit themselves and disadvantage their opponents.
In states with a large number of districts, such as Pennsylvania, the leeway afforded to lawmakers is huge. After the 2010 Census, for instance, Pennsylvania Republicans drew a map that created 13 safe Republican seats and five Democratic ones: three in Philadelphia, one in Pittsburgh and one encompassing the Scranton/Wilkes-Barre region in the northeast part of the state.
The map is drawn in a way to make it highly unlikely that any seats will switch political parties or that Democrats, who tend to win about half of the statewide popular House vote, will capture more than five seats. As testament to the effectiveness of the gerrymander, not a single seat has switched parties in the three House elections held since the redistricting.
But of course it doesn't have to be that way. Had the Democrats been in power at the time of redistricting, they could have drawn a map to give themselves a maximal advantage. According to FiveThirtyEight's Atlas of Redistricting, for instance, it's possible to draw a map that includes nine safe Democratic seats, a net gain of four seats.
Relative to the current map, this one squeezes two additional Democratic seats out of Philadelphia, one more out of Pittsburgh and one more in the eastern half of the state.
FiveThirtyEight's number-crunchers also tried to improve on the current Republican gerrymander. They were able to improve Republicans' already high odds of winning in some districts but were unable to do better than the current 13-to-5 Republican split. That gives some sense of just how aggressively the existing map favors the GOP.
A four-seat shift is huge in a state with 18 districts. Given the sharp and narrow political divides in Congress these days, changing the partisan makeup of just one state's House delegation has the potential to bring national consequences. Multiply this across the entire country and it becomes apparent that you could radically reshape the future of the House of Representatives simply by changing the locations of a few lines.
In North Carolina, for instance, you could turn the current 10-to-3 districting in favor of Republicans into an 8-to-5 Democratic majority. Conversely, in Maryland you could turn the existing 7-to-1 Democratic advantage into a 4-to-4 split.
Add it all together, and nationwide, according to FiveThirtyEight's calculations, the exact same election could produce a 65-seat Democratic advantage in the House, if every single state were gerrymandered in Democrats' favor, or a 92-seat Republican advantage under an aggressive nationwide GOP gerrymander. The difference between those outcomes is the amount of leeway state legislators have to alter our political future by drawing their own political boundaries.
We tend to think that voters choose their representatives, making Congress a reflection of the will of the people. But, in reality, much of the makeup of the House is a product of politicians choosing their voters.