The Republican Gerrymander Might Lose It’s Devil’s Bargain

Chris has graciously allowed me to submit a guest post, so I thought I’d do one about gerrymandering and why it’s particularly fascinating for this election cycle.

Those reading the title might expect me to say the devil’s bargain is tampering with the democratic process, or some other moral argument against gerrymandering. While there are lots of such arguments with lots of merit that should be debated (and indeed, several courts are considering that very point as we speak), this will not be one. It’s a purely inside-baseball deep-dive into the dark art of gerrymandering itself, and the numbers and statistics that are its bread and butter, along with my humble notes about some interesting phenomena that might occur this cycle as a result of the current map.

So what exactly is the devil’s bargain then? It is this: gerrymandering allows you to win close elections, but makes you more susceptible to being washed out in wave elections. The basic idea of gerrymandering is that you make your opponent “waste” votes by packing his voters into a few districts. And then, you spread your voters around as thinly as possible, capturing 51% of the vote in as many districts as possible. That’s why in Republican gerrymandered states, Dem strongholds in cities frequently rack up 90% Dem majorities (in fewer districts), while Republican districts skate by with 55% majorities or less (in more districts). At the end of the day, it doesn’t matter what your vote totals are as long as you’re at >50%.

That’s the good side of gerrymandering. The downside is evident by looking at the above numbers closely: thanks to packing, the Dems will never lose their 90% majority seats. Meanwhile, if the election swings 5%, the Republicans lose *all* their seats. And that’s the Devil’s bargain: the more aggressively you spread your voters to maximize your seats in regular elections, the fewer votes you have to serve as a buffer against a wave.

Another phenomenon to understand is that this is not a linear process. In our simplified example above, the Republicans lose *no* seats until the Dems hit 55%, and then, they’ll lose *all* of them. IOW, the Republicans in this example have a “firewall” that can withstand up to a 5% wave, but then get entirely washed away with anything more than that. Of course, this is a hypothetical example, but it holds in the real world.

When politicians decide their gerrymander, they decide how aggressive they want to be, and how much “reserve” they put in each district to withstand wave elections, population shifts (remember districts have to hold for 10 years), etc. Oftentimes they even take into account the actual politician holding the seat right now. If he’s a popular incumbent who’s expected to stay in office for 10 years, then he needs less reserve. He might even have enough bipartisan support that you can make his district minority Republican. OTOH, if it’s a district with a new Congressperson, or an old guy who’ll likely retire in a few years, then you might put a few more Republicans in their districts to help them out. Of course, there are backroom negotiations for all of these: while everyone agrees in theory to spread out voters to maximize district wins, each individual politician wants an easy district, with tons of supporters, which means sometimes a powerful Congressman gets to keep a bunch of voters he doesn’t need, just so he can sail through his elections.

At the end of the day, all of these individual decisions (and I do mean individual: districts are frequently drawn down to the block and sometimes individual house level; often to exclude a popular incumbent from a district that contains his vote base) lead to the national map that we now have.

So with that background, just how does that national map look? Is there a linear progression of districts? That is, for each 1% gain in vote share, does a party’s district total increase linearly? Is it exponential? Or does the firewall concept I described above apply?

In order to answer this question, we have to first ask: at each level of partisan breakdown of the national vote, how many districts will the Dems hold? And for each increase of 1% in the vote total, how many additional seats will the Dems get? If there is no gerrymandering, this should follow a normal distribution. That is, you’ll see a large number of districts change hand right around the 50/50 mark and fewer districts as you get to the extreme. For example, if you’re at 90%/10%, there aren’t many more districts left for you to win, so each extra percentage point increase in your vote total won’t bring all that many additional seats. At 50/50, there should be a ton of districts that will swing with just small changes in vote totals. This is what you’d expect without any gerrymandering.

But how would a graph look in the firewall concept above? In that hypothetical example, between 50%-54% vote share, the Dems get zero additional seats with each 1% increase in vote share. But at 55%, they get *nine* with the next 1% increase in vote share.

Can we make similar calculations for the national map? Turns out we can. The Cook Political Report publishes a commonly used metric, called the Partisan Voting Index (PVI). This measures partisan lean compared to the national average. So for example, a district that is D+5 leans 5 percentage points more towards Democrats than the national average. In an ideal world, all districts would be +0, i.e. their partisan lean is no more or less than the national average. Which means the PVI is a useful indication of how badly gerrymandered a district is (although it’s not perfect; there are other factors besides gerrymandering that affect PVI. For example an incumbent who’s popular with both parties might get more votes than the national average, which will give him a large PVI). In graph 1, I’ve taken the PVI of each district and plot it on a graph. As the Democratic vote total goes from -50 (i.e. they underperform the national average by 50 points) to 0 (i.e. right at the national average) to +50, you can see how the total number of districts the Democrats win changes as their national vote total changes. At 0, you can see that the Democrats don’t get a majority, which is confirmation of the Republican gerrymander. Indeed, they aren’t predicted to get a majority until they hit about +5%.


Next, we get to graph 2, the key graph. This shows the number of additional seats the Democrats can expect to win with an additional 1% increase in vote share *at each level of vote share*. I believe a clear firewall effect can be seen, and to see it, I’ve added annotations.

Graph 2: Number of Additional Seats Gained Per additional +1 PVI

The blue dotted line shows a normal curve that we should expect to see if there was no gerrymandering. And in the extreme left and right, the graph largely conforms to this. However, in the middle, where most gerrymandering takes place, you’ll see a marked difference. At the zero point (i.e. 50/50 vote share), the number of districts that change hand decreases. To the left of that point, you can see that the number of seats lost by Dems drastically decreases for a few percentage points, until their firewall breaks. After that, as you follow the graph left, the number of seats lost drastically increases with each point until it settles into the expected normal curve beyond the gerrymandered seats. That means the seats within the green oval have been gerrymandered to withstand a wave election. To do so, the districts in the red oval have been made *more vulnerable* than they would normally be. This is the devil’s bargain inherent in all gerrymandering.

How about the Republicans? If you follow to the right of the zero point, the Republican gerrymander can be seen as well. For the first 5-7% vote shift, while there are districts changing hands, the number of such districts is less than expected, thanks to gerrymandering. However, the price for that gerrymandering is that the districts slightly to the right of that (in the red oval) become extraordinarily sensitive to a wave. Which means that if Dems are able to push beyond the wall, they may see *increased* number of districts falling their way. Normally, it would be the opposite: as you get further from 50/50, the law of diminishing returns sets in and you see fewer pickups.

Based on this graph, I assert that the Republican gerrymander breaks between about 8-15% wave election. While the firewall isn’t absolute (districts do change hand even below those percentages), the number of districts that change drastically increase once the firewall is broken, more than if the gerrymander wasn’t there in the first place. Which means the two most likely scenarios is that either the Dems fail to breach the firewall and remain in the minority (albeit with a smaller gap), or they break the firewall and gain a large majority. Ironically, it’s less likely that they get to a bare majority and stay there.

So far, the polls and results seem to point to the Dems being at the cusp of breaking this firewall. Generic Congressional ballots have had the Dems up 6-12 points. Meanwhile, in special elections thus far, Dems have been running about 16% ahead of their previous performance. This has held even in high-turnout elections like the AL-Sen and the PA house district races.

In summary: until about 8% advantage, the Dem wave will be crashing against the Republican gerrymander. While that may be enough to stagger to a tiny majority, it’s also very possible (maybe likely) they end in the minority even with that voting advantage. However, from 8% to 15%, it turns into a tsunami, where even relatively small increases in Dem voting percentages will yield enormous numbers of districts. If the Dems can push beyond that barrier, thanks to the Republican gerrymander, the Dems may be looking at a very, very comfortable majority, one they wouldn’t have had if the Republicans left their districts alone. The polls suggest they may be right around the cusp. Which means after all these years, the Devil may finally be knocking at the Republicans’ doors, collecting his due…


  1. Winning a PVI of +8 means winning an election by *16* points because R+8 means also D-8. So the Republican gerrymander starts to break when the Democrats win by 16 points. By that point the Dems would have a clear majority anyway even dealing with the gerrymander (the majority comes at about the start of R+4 seats). In addition, you have to go well past the firewall for the extra seats gained at that point to make up for the firewall seats not gained at lower PVI, so the cost of the gerrymander is basically nil.

    1. No, it just means 8%. Because for each point the Ds gain, the Rs correspondingly lose a point. Otherwise, where do the votes come from? 🙂

      For example, if the national average was 50/50 vote share, then a PVI of R+8 implies the house district broke as 58/42. That does indeed work out to a 16% difference. But if the Dems gain 8%, they get to 50%, while the Rs decline to 50% at the same time.

      It’s the same math that says that while the Dems are currently down ~45 seats in the house (238 R; 193 D; 4 vacant), they need ~20 seats to gain the majority.

    1. However, bucking the GOP gerrymander firewall is not seen as likely.

      “But from a national perspective, Democrats seeking to regain a House majority will likely face the same anti-competitive districts that they have seen since 2012. Despite close statewide popular vote results, the GOP typically wins more seats.

      “Because of maps designed to favor Republicans, Democrats would need to win by a nearly unprecedented nationwide margin in 2018 to gain control of the House of Representatives,” the Brennan Center for Justice at New York University Law School said in an analysis released before the Court’s hearing. “To attain a bare majority, Democrats would likely have to win the national popular vote by nearly 11 points. Neither Democrats nor Republicans have won by such an overwhelming margin in decades. Even a strong blue wave would crash against a wall of gerrymandered maps.”

  2. In other news about overreach, Sinclair Broadcast Group made the wizard behind the curtain way too obvious:

    Please actually watch the video. It’s great editing, makes a very specific and clear point that delivers an effective message to the audience and makes it difficult to look away from.

    My available time and energy for going into deeper analysis is slim but I’m going to watch this for a bit and see if anything interesting comes of it.

      1. In a prior post by Chris, “How to Win Elections in America,” he states: “Republicans are the modern masters of bribery and fear. Their fear pitch is basically this – Vote for us, or brown people will rampage through your neighborhood and take all your stuff. Their bribery pitch is just as sick – Vote for us and we’ll strip the republic down to bare pipes and wires, but we’ll give you a small cut of the loot. It isn’t much, but it’s better than nothing. And it’s winning.”

        Who can’t see the connection between this statement and what is happening in America today? The Sinclair “fake news” initiative is merely an extension of the attack Trump launched in his campaign and is perpetuating through his appointees. The Republican Party is contributing by completely ignoring their responsibility to serve as a check and balance of the executive branch. They have embraced the whole sordid scheme, abandonning any pretext of concern for democratic values for all people much less conservative principles. Look at the list: ending net neutraility (freedom of speech); introducing fake news (control of message); disparagement of immigrants (brown people); attacks on women’s rights (subjugation to restore patriarchal control); attacks on our justice system (legal accountability of the system); overt racism (inferior people); suppression of the vote (election control); destruction of health care (the ultimate fear tactic for families); purge of climate change mitigation and research (fossil fuel pay-back); expansion of income and wealth distribution that is destroying America’s middle class. Sinclair is only one tool in their kit to retain power and control. The hell with anything or anyone else. These are not nice people. They intend to win whatever it takes. Chris is right.

        Republicans are laser-focused on protecting their majority control of the U.S. House in the November, 2018 election. They have not completed their agenda, as Paul Ryan candidly stated in a recent FOX interview. (This 7′ interview is well worth your time.) The GOP will employ everything they can to retain control, including talking points that debunk “fake news.” After all, Republicans know all about fake news – they perfected the art.

    1. As you know, Dins, I have been watching Sinclair activities with concern for some time. Why control just one news outlet when you can control them all? It’s mind-blowing and demonstrates the ability of Republicans for large-scale planning through whatever means will work. FOX clearly has shown the willing blind acceptance of FOX commentary as “news”, why not expand thought control to the national stage?

      The montage of FOX newscasters parroting the fake news script is brilliantly constructed. It is horrifying and sad to see professional media figures parrot the messages as they go about their jobs. It is more horrifying to speculate on how effective this strategy by Sinclair will be. One wonders if Roger Aisles could be lurking in the background of this effort, given his hard-right politics, deep relationship to Trump, and his knowledge of the industry? Regardless, the scope of the Sinclair expansion involves a lot of planning and cooperation, as the inset article describes (linked below) – aided and abetted by the appointment of Ajit Pai as Director of the FCC. Literally, the fox is guarding the hen house.

      The Sinclair initiative has been moving steathily in the background. Can it be stopped at this point? Does anyone care?

      1. Mary, the difference between the two-headed media monster (Fox and Sinclair) and Pravda and the Nazi control of German media is zero. And interesting history of how the Nazi’s took control of German media.

        There are any number of people that would go back in time and kill all the major players in 1930’s Nazi Germany, but so few willing to kill the major players today. Why is that? History is replaying itself, and we are accelerating towards Orwell’s nightmare.

    2. One more article that addresses Sinclair. I am surprised at the contract provision that penalizes news anchors with 40% return of salary if they quit before their contract ends. It is also noteworthy that the spiels have two objectives: spreading the fake news alarm and making the viewers believe their network is the only credible news source. George Orwell must be rolling over in his grave……

    1. A viable concern, but the trend in special elections (as Wall mentioned, in either low-turnout or high-turnout races) speaks, perhaps, to an underlying Democratic advantage that the polls aren’t capturing. Key to victory in the midterms often comes down to how enthusiastic your own voters are and how depressed the other side is.

      What’s key here isn’t that the polls are unreliable, but that they predict turnout based on past elections – and so if you’ve an orange troll in the WH that’s produced a sudden and immediate change in voter turnout, the polls aren’t going to be able to capture that, not completely at least.

      1. Special election wins for the Dems have been encouraging, and I believe reflective of the national drift to a more liberal orthodoxy; however, the real test will come in the highly gerrymandered districts. 538 is forecasting about a 6% lead for Democrats which we all know is not enough to re-take the House, which is our best hope in the mid-terms. The wild card are the Independents. If this group swings left, there is a chance to move that single digit lead into the double digit category that will be needed to produce a “blue wave”. Republicans obviously do not believe that will happen, given the strong economy, their lock on gerrymandered districts, and the typically low mid-term turn out, bolstered by predictably consistent Red base turnout.

      2. If Republicans were honestly confident about the economy and the tax cut bolstering their chances, then that’s what they would’ve run on in the former PA-18, an otherwise overwhelmingly Republican district – and yet they utterly abandoned all that, instead turning to immigration, Nancy Pelosi, and other grievance-based ‘issues’ to gin up turnout. It all failed.

        Furthermore, in addition to strong candidates and campaigns, one of the most critical elements to midterm success is enthusiasm, and in that regard, Dems have been up over 20+ points over Republicans – not to say that they’re going to get anywhere close to that, but I’d argue it’s more accurate to take that, the generic ballot, and some other measures to get a more accurate picture of what we can expect going into November.

      3. The Republicans initially tried to run on the tax cut and the economy, and it flopped, so they switched to the tried-but-apparently-no-longer-true “Demon Pelosi” tack. It seems they believe their own nonsense, but fortunately it looks like a clear majority of voters don’t.

  3. EJ

    That’s very interesting, Wx Wall. Thank you for taking the time to go through the maths.

    As you point out, this makes it very unlikely that there will ever be a bare Democrat majority: either the swing is large enough to overwhelm the firewalls or it isn’t.

  4. Very goop post WX. It describes the basic problem with gerrymandering very well. Your conclusion that the D’s are at the cusp of breaching the R’s firewall is very much to the point. As Mary repeatedly states and emphasizes, GOTV is going to be very important this election. If the the D’s mount a thorough GOTV drive nationwide this cycle, breaching the wall will be far easier.

    I see that happening in WA state. Even though we are nominally a blue state, we still have 4 of 10 R CDs. My estimates and comments on each follow:
    1. 8th CD – Even PVI, open and will probably flip. R’s have very strong candidate and are pouring money into the district. D’s also have two very strong candidates; both are well financed.
    2. 3rd CD – PVI R+4, possibly could flip, but the D’s do not seem have a really strong candidate.
    3. 5th CD – Cathy McMorris-Rodgers, PVI R+8, really strong D candidate, good possibility of flipping, on D target list.
    4. 4th CD – PVI R+13, not likely to flip but D’s are actually running a good candidate and we may have both a D and a R on the General Election ballot. WA is a top two state.

    With this lineup, GOTV will be very important in the 8th, 3rd and 5th. I consider the 8th basically an exurban and rural district. Also WA is only mildly gerrymandered so the R’s have a higher firewall. Even an extreme R gerrymander would only reliably give the R’s 5 districts.

    CA is also key this election cycle. There are several CD’s that are at risk of flipping and there is likely to be a strong – possibly even tsunami – blue wave this cycle. I truly hope there is a very strong GOTV effort there. PA will be important too. TX could also be important.

    Finally, what SCOTUS decides in June is going to be important, but I am dubious the decision will change the maps by November.

Leave a Reply