Sabatos Crystal Ball

The Electoral College: Expanding the Map

Trump is at least a small underdog in all the Clinton states, but trying to play offense is wise

Kyle Kondik, Managing Editor, Sabato's Crystal Ball September 19th, 2019



— We don’t really think President Trump can win New Mexico, where he campaigned earlier this week. But he’s wise to try to expand the map.

— While presidents who lose reelection historically don’t win states they didn’t carry in their earlier victories, presidents who win reelection typically do end up winning one or more states they lost previously, although there is one significant recent exception.

— However, the president seems to be at least a small underdog in every Hillary Clinton-won state. We’re moving New Hampshire from Toss-up to Leans Democratic in our Electoral College ratings.

Table 1: Crystal Ball Electoral College rating change

State Old Rating New Rating
New Hampshire Toss-up Leans Democratic

Trump tries to expand the map

President Trump was in New Mexico earlier this week in service of what seemed to many like a quixotic mission: Flipping the Land of Enchantment from blue to red in 2020.

New Mexico voted for Hillary Clinton by about eight points in 2016; the state voted for Barack Obama by about 10 points four years earlier, a slight shift to the right that mirrored Obama’s four-point national popular vote victory falling to a two-point margin in favor of Clinton in 2016.

In other words, New Mexico didn’t show any particularly strong trend toward Republicans in 2016, and nothing in the 2018 results, when Democrats swept the state’s federal and statewide races, suggested otherwise. One wild card, though, is that Libertarian Gary Johnson attracted a significant share of the vote in his home state’s presidential race in 2016 (9%) and Senate contest in 2018 (15%), a sizable bloc of voters Republicans hope will significantly break toward them without Johnson on the ballot.

Still, New Mexico also has the largest percentage of Hispanic voters of any state, a group that as a whole is considerably more Democratic than non-Hispanic whites. Clinton also won 48% of the vote in New Mexico in 2016, meaning that Trump (who got 40%) likely would have to convert the lion’s share of the Johnson voters to his side in 2020 in order to win the state. In 2018, Sen. Martin Heinrich (D-NM) was reelected with 54% of the vote, meaning that even if all the Johnson voters had voted for the GOP nominee instead, Heinrich still would have won comfortably.

We rate New Mexico as Likely Democratic for the 2020 presidential general election at this early juncture: Not a total slam dunk for Democrats, but not a true swing state either, in our judgment.

However, that is all a long preamble to a larger point: Trump and his team are wise to try to expand the electoral map.

Remember: Trump was outraised by Hillary Clinton in 2016, but this time he may very well enjoy a resource advantage over the Democratic nominee, and therefore he can afford to pump more money into non-essential states than last time. Even if he’s ultimately bluffing in New Mexico, there are at least three other Clinton states — Minnesota, New Hampshire, and Nevada — that were significantly closer than New Mexico (all were decided by 2.5 points or less) where Trump likely will make a significant effort. Don’t necessarily assume he can’t win one or more Clinton-won states, even as we see him as an underdog in all of them (more on this below).

Overall, if Trump loses reelection, history suggests that he won’t win any states in 2020 that he lost in 2016. But if he wins, he very well may win one or more states he didn’t win last time.

In the current two-party presidential era — which dates back to 1856, when the Republicans first produced a presidential nominee who was the main rival to the already-existing Democrats — six incumbent presidents have lost a general election for a second term after winning a first term in the previous election: Grover Cleveland (D, 1888), Benjamin Harrison (R, 1892), William Howard Taft (R, 1912), Herbert Hoover (R, 1932), Jimmy Carter (D, 1980), and George H.W. Bush (R, 1992).

None of them carried any state they lost four years prior. Of course, this makes intuitive sense: If a president goes from winning to losing, he is by definition losing ground. So all of these losing presidents lost states they had carried four years prior (in some instances, they lost quite a lot more).

However, if Trump wins, history suggests that he might win one or more states he didn’t carry last time.

Again, since 1856, there have been 11 incumbent presidents elected to a second term after winning a first term in the previous election. (This omits presidents like Theodore Roosevelt and Lyndon B. Johnson, who won elected terms in their own right after taking over for presidents who died in office, and also Cleveland, who won in 1884, lost in 1888, and won again in 1892.)

These 11 were Abraham Lincoln (R, 1864), Ulysses S. Grant (R, 1872), William McKinley (R, 1900), Woodrow Wilson (D, 1916), Franklin D. Roosevelt (D, 1936; we are omitting his third and fourth elections for the purposes of this discussion), Dwight D. Eisenhower (R, 1956), Richard Nixon (R, 1972), Ronald Reagan (R, 1984), Bill Clinton (D, 1996), George W. Bush (R, 2004), and Barack Obama (D, 2012).

Of these 11 reelected presidents, 10 won at least one state they failed to carry in their initial successful election. The one exception is the most recent reelected president, Obama, who lost Indiana, North Carolina, and the single electoral vote contained in Nebraska’s Second Congressional District after somewhat surprisingly winning these in 2008, and he didn’t add any new electoral votes to his coalition. That historical oddity makes more sense when one considers that Obama was the first president reelected to a second term to lose ground in his popular vote share since Andrew Jackson (again, this omits FDR’s final two reelections, as well as Cleveland’s 1892 victory after a four-year hiatus).

Interestingly, of these reelected presidents, a majority (seven of 11) lost one or more states they had won in their first successful election. Obama, as mentioned, was one; George W. Bush was another: He picked up Iowa and New Mexico from four years prior but lost New Hampshire. In 1996, Bill Clinton lost Colorado, Georgia, and Montana after winning them in 1992, but he more than made up for those lost electoral votes by flipping Arizona and Florida from the Republicans.

We are in an era with many landslide states in the Electoral College, and we probably should expect a good amount of stability in state-level voting from 2016 to 2020. However, things can and will change.

Obviously, if Trump loses, he will lose some states he won in 2016, and his intense focus on motivating his base over expanding it may make him an unlikely candidate to flip a Clinton 2016 state in defeat. However, if Trump wins, history suggests he might both gain and lose ground; hypothetically, it’s not hard to imagine him, for instance, losing Michigan but winning New Hampshire. These were the two closest states in 2016 and were decided by less than four-tenths of a percentage point apiece: It wouldn’t take that much to flip either one way or the other.

The Electoral College picture now

We continue to see the 2020 presidential election as something of a 50-50 proposition. There are competing trends that argue both for and against the president’s chances. On one hand, an incumbent president presiding over a time of relative peace and prosperity usually would be seen as a favorite, although there is some question about whether Americans’ optimism about the economy is weakening. The president does not have a top-tier challenger for the GOP nomination, another factor in his favor. On the other hand, the president’s approval rating is consistently weak, weaker than an incumbent president would want going into a reelection bid, and it’s not even clear that everyone who approves of the president’s job performance is certain to back him next year.

Without knowing the identity of the Democratic nominee, and without knowing the future shape of the economy and a number of other factors, the best thing to do (in our opinion) is to look at the race as close and competitive for now, as presidential elections have mostly been in recent years and as an acknowledgement of the competing electoral indicators.

We are formalizing that to some degree in our Electoral College ratings by making one slight adjustment, moving New Hampshire from Toss-up to Leans Democratic. The Granite State is almost always competitive, but Trump’s approval there has generally been weak. Throughout 2018, Gallup measured Trump’s approval in New Hampshire at 35% approve, 58% disapprove; more recently, Morning Consult found his approval rating 20 points underwater. The University of New Hampshire’s Granite State poll (42% approve/53% disapprove) and Gravis Marketing (44%/54%) from earlier this summer are better but still weak for the president. So this trend isn’t really new, but in reassessing our ratings, we thought it was more appropriate to list New Hampshire as Leaning Democratic. Meanwhile, in the state’s Senate race, it appears that former Trump campaign manager Corey Lewandowski (R) is getting closer to entering the race to challenge Sen. Jeanne Shaheen (D-NH). A Lewandowski nomination would certainly represent a double down on Trump Republicanism in New Hampshire, even though the notoriously fickle state may be moving away from the president.

That makes the overall Electoral College ratings exactly split, 248 apiece, with 42 electoral votes’ worth of Toss-ups: Arizona, Pennsylvania, and Wisconsin, plus Nebraska’s Second Congressional District.

This also puts all of Clinton’s 2016 electoral votes in at least the Leaning Democratic column. But that doesn’t mean the president shouldn’t target some of these states anyway — and he certainly will.

Map 1: Crystal Ball Electoral College ratings

Biden’s challenge: Iowa and New Hampshire

The schedule advantages Biden’s rivals, although it’s unclear if they can capitalize; NC-9 fallout

Kyle Kondik, Managing Editor, Sabato's Crystal Ball September 12th, 2019



— Perhaps the biggest threat to Joe Biden is the nominating calendar.

— Biden is reliant on support from African Americans, but the electorates of the first two states, Iowa and New Hampshire, are almost entirely white.

— However, even if one or more of Biden’s rivals best him in the leadoff states, they may not necessarily have much appeal to the crucial African-American voting bloc themselves.

Iowa, New Hampshire, and Biden

As Democrats prepare to debate tonight, the Democratic race remains largely as it has been. Joe Biden is leading, but the other candidates are preparing — and hoping — for him to eventually fall off. It is anyone’s guess as to whether this will actually happen. Democrats hoping for Biden to collapse may find themselves in the position of Donald Trump’s opponents from four years ago by acting out their own version of Waiting for Godot — anticipating the arrival of something that never actually arrives.

If Biden retains his lead into next year, though, it may be that the thing that ultimately trips him up is the Democratic nomination calendar.

While Biden’s lead is built on support from African Americans, hardly any black voters will participate in the first two contests: the Iowa caucus on Feb. 3 (the day after the Super Bowl) and the New Hampshire primary on Feb. 11. According to the 2016 exit polls, the Democratic electorates in both states were over 90% white.

The opportunity that these two overwhelmingly white electorates present to the other candidates is obvious, based on the current demographic bases of support for Biden and his two current leading rivals, Bernie Sanders and Elizabeth Warren.

According to the most recent Economist/YouGov poll, Biden leads with about 40% among African-Americans nationally, while Sanders, Warren, and Kamala Harris are well behind at around 10% apiece. Meanwhile, Warren leads with white voters with 26%, with Biden (18%) and Sanders (16%) behind her. An ABC News/Washington Post poll released over the weekend tells a similar story: Biden was at 38% with the broader universe of nonwhite voters, with Sanders at 19% and Warren at 12%. Meanwhile, the three top candidates were all at around 20% with white voters.

According to the most recent Economist/YouGov poll, Biden leads with about 40% among African-Americans nationally, while Sanders, Warren, and Kamala Harris are well behind at around 10% apiece. Meanwhile, Warren leads with white voters with 26%, with Biden (18%) and Sanders (16%) behind her. An ABC News/Washington Post poll released over the weekend tells a similar story: Biden was at 38% with the broader universe of nonwhite voters, with Sanders at 19% and Warren at 12%. Meanwhile, the three top candidates were all at around 20% with white voters.

Biden’s team is already lowering expectations for Iowa and New Hampshire, and perhaps rightfully so. One would suspect Iowa and New Hampshire to be among the most challenging states in the country for a candidate like Biden given the racial disparities in his levels of support. The danger for Biden is that he might lose both states, which could prompt a ripple effect that would hurt him elsewhere. Nevada votes next, on Feb. 22, followed by South Carolina on Feb. 29. The Silver State will provide the first real test of the preferences of nonwhite voters (in 2016, its caucus electorate was split about 60% white to 40% nonwhite) and the Palmetto State will show how southern African Americans, a vital voting bloc, are leaning: That electorate should be about 60% black.

Super Tuesday follows on March 3, and by March 17 about two-thirds of the delegates will have been awarded.

The past two contested Democratic presidential nomination battles showed how Iowa and New Hampshire may — or may not — change the race. Hillary Clinton’s failure to sweep Iowa and New Hampshire helped open the door to Barack Obama in 2008, while Clinton’s narrow Iowa win and blowout New Hampshire loss to Sanders in 2016 did not really threaten her hold on the nomination.

A key difference between Hillary Clinton’s main challengers in 2008 and 2016 was that Obama, as a dynamic African-American politician, had a lot of growth potential among black voters. Following his victory in Iowa, which showed his national viability, he turned this potential into reality, riding big margins with black voters to a narrow national victory over Clinton for the nomination. Eight years later, Clinton’s main opponent, Sanders, was unlike Obama in that he did not possess obvious appeal to African Americans. Clinton’s black support held in South Carolina and in later contests, and she won the nomination comfortably.

One factor that might bolster Biden if he struggles in Iowa and New Hampshire is that if Warren and/or Sanders edge him out in those states, neither of those candidates may be able to capitalize on those victories by boosting their support with African-American voters, as Sanders failed to do in 2016. In other words, Biden may be able to survive losses in both states, although his potential ability to do so would be historically strange: Since 1976, nearly every nominee for either party won at least one of Iowa or New Hampshire. The sole exception was Bill Clinton in the 1992 Democratic contest, although that race deserves something of an asterisk because the other Democratic candidates (including Clinton) essentially forfeited Iowa in deference to home-state candidate Sen. Tom Harkin.

The possibility exists that Biden could be the second.

But this also points to intriguing other alternatives, such as the possibility that if Biden falters, his black support could become splintered — which might open up the path to the nomination for whichever one of Warren or Sanders comes out of Iowa and New Hampshire better positioned than the other — or perhaps migrate to someone other than Warren or Sanders. This possibility surely sustains the candidacies of African-American candidates Kamala Harris and Cory Booker, whose respective paths to the nomination are very much like Obama’s on paper: Win or exceed expectations in Iowa and/or New Hampshire, and boost their African-American support as a result. The problem for both is that, in addition to having to contend with the other, Harris and Booker are way behind Obama’s progress from 2007, where by this time in the race he had established himself as the clearest challenger to Clinton. Harris and Booker have done nothing of the sort, and they are languishing behind not just Biden, but others as well.

The North Carolina fallout

Republicans held the closely-watched do-over special election in NC-9 on Tuesday night, as Rep.-elect Dan Bishop (R) defeated veteran and 2018 nominee Dan McCready (D) by about two points.

Both sides had reasons for optimism: Republicans held the district, and Bishop should have an easier time defending it as an incumbent next year and with presidential-level turnout. From that standpoint, Republican outside forces may not have to pump money into the seat, which means that they could use those resources elsewhere. Had McCready won, Republicans may have been able to reclaim the district next year, but it would have come at considerable expense. President Trump can also plausibly claim that his Monday night rally in Fayetteville helped push Bishop over the finish line, although specifically quantifying the effect of such rallies on any contest is difficult. Our new rating for NC-9 for next year is Likely Republican.

Meanwhile, Democrats could point to McCready considerably outperforming Hillary Clinton’s 12-point loss there in 2016, which was a positive theme for Democrats in special elections last cycle. While the president’s efforts on behalf of Bishop may have helped, Trump’s overall unpopularity once again threatened GOP control of a district that is not as competitive on paper as Tuesday night’s result indicated. The result was fairly similar to that in last year’s OH-12 special election, a district that Republicans also narrowly held but where the Democrat ran about 10 points in margin ahead of Clinton’s 2016 showing. Those two races (OH-12 last year and NC-9 this year) were also similar in that Democrats shot out to early leads based on Democratic-leaning early votes, and Republicans made up sufficient ground on Election Day. That is the usual pattern in North Carolina and Ohio, as well as Florida and some other states.

Republicans also ended up easily holding NC-3, the night’s other special election. In fact, Rep.-elect Greg Murphy (R) won by 24 points, matching Trump’s showing from 2016 and providing Republicans with a helpful data point. That race is Safe Republican for next year.

One thing to watch in North Carolina going forward is whether Democrats attempt to use their power on the state Supreme Court to force a re-draw of the state’s Republican-drawn congressional gerrymander. The court just threw out the state’s legislative districts, although there might not be sufficient time for a similar lawsuit and ruling on the state’s congressional districts to impact 2020 elections.

The NC-9 do-over wraps a bow (finally) on 2018’s House elections. In the end, Democrats won 235 seats and Republicans won 200. In 2016, Republicans won 241 seats and Democrats won 194, so the Democrats netted 41 seats from November 2016 to November 2018. To win the House back, Republicans will have to net 18 seats, although that number may actually be 19 — remember that Rep. Justin Amash (I, MI-3) left the GOP earlier this summer, meaning that Republicans will have to defeat him in order to be 100% sure that the seat’s occupant would back a Republican in the 2021 speaker vote.

Table 1: Crystal Ball House ratings changes

Member/District Old Rating New Rating
Greg Murphy (R, NC-3) Likely Republican Safe Republican
Dan Bishop (R, NC-9) Toss-up Likely Republican

The House’s Republican Bias: Does it Exist?

Two measures tell two different stories

Seth Moskowitz, Guest Columnist, Sabato's Crystal Ball September 12th, 2019



— Single-member districts, natural sorting, and gerrymandering are the origins of bias in the House of Representatives.

— One form of bias consistently helps House Republicans, vindicating liberal concerns of a structural imbalance. Another form of bias reliably benefits the party that wins control of the House, disrupting claims of a Democratic disadvantage.

— If Democrats keep their current 7.6% (53.8%-46.2%) lead in the two-party Generic Ballot through November 2020, they will probably hold the House and win more than the proportionate 53.8% of House seats (234 seats).

Structural bias in the House

The Republican Party’s structural advantage in federal elections has been well documented in liberal circles. Democrats argue that Republicans have so heavily gerrymandered the House that the institution’s legitimacy is at stake.

But do Democrats really face a structural disadvantage in House elections? Two measures of bias — the Median District Bias and the Seat Bonus Bias — tell two different stories.

The origins of bias

The House’s biases stem from its composition of single-member districts. This conception of the House — 435 individual districts with one representative each — is not mandated by the Constitution. The Constitution stipulates that states have House representation proportional to their population and that each state receive at least one representative. As for elections, the Constitution says only that these representatives should be “chosen every second Year by the People of the several States.”

Instead, it’s the Uniform Congressional District Act, a federal law passed in 1967, that requires single-member districts. Hawaii and New Mexico received exceptions to continue electing representatives at-large, but both have done away with the practice. The House is now uniformly composed of single-member districts.

Single-member districts mean that a vote cast for a losing candidate will not be represented. Similarly, a vote cast for a candidate over the threshold needed to win is electorally useless. Both of these votes are, to use a harsh term, “wasted votes.” Democrats cast more wasted votes than Republicans due to an imbalance in how party members are distributed among districts. This imbalance is a result of both natural sorting and political gerrymandering.

Natural sorting describes how members of the two parties are distributed across the country. Democrats are heavily concentrated in cities and urban areas; Republicans tend to be scattered among rural, exurban, and suburban districts. There are more districts with very high concentrations of Democratic voters than there are districts with very high concentrations of Republican voters. This Democratic density makes it easy to win individual seats but creates lots of wasted votes. Research by political scientists Jonathan Rodden and Jowei Chen, as well as Rodden’s new book, Why Cities Lose, show that geography and natural sorting are the root of Democrats’ electoral challenges.

Political gerrymandering is the manipulation of electoral districts to favor one party over another. States where one party controls the process often attempt to maximize their party’s representation using tactics called “packing” and “cracking.” Packing is drawing districts to heavily overrepresent the opposition party, wasting as many votes as possible over the winning threshold. Cracking is the opposite: diluting the opposition’s voters into districts so they cannot reach the threshold. Most statewide gerrymanders are a combination of packing and cracking.

Natural sorting and gerrymandering can only distort House representation away from the national popular vote because we use single-member districts. Together, single-member districts, natural sorting, and gerrymandering form the origin of bias in the House.

The Median District Bias

The Median District Bias estimates the margin by which a party needs to win the national popular vote (this analysis uses the overall House popular vote unless otherwise stated) in order to win control in the House. If you lined up all the districts from most Democratic to most Republican, the median House district would be directly in the middle: number 218 out of 435 if no third party or independent candidates won seats. This district would tip control of the House. The gap between this district’s margin and the national popular vote is the Median District Bias.

Let’s take an example. In 2018, Democrats led the national popular vote by 8.6% (53.4% to 44.8%). Democrat Josh Harder won the median House district, California’s 10th, by 4.6% (52.3 to 47.7). If the whole nation voted 4.7% more Republican, Democrats would have lost CA-10 and control of the House while winning the national popular vote by 3.9%. So Republicans had a 3.9% Median District Bias.

Uncontested districts change this analysis slightly. The national popular vote does not include voters who would have voted in the House elections but did not because there was no candidate from their party running. When these phantom voters are accounted for, Democrats still won the 2018 popular vote by 7.3%, which means Republicans had a 2.6% Median District Bias.

Another way to avoid the problem of uncontested districts is to use the presidential popular vote instead of the House popular vote. Democratic and Republican voters will always have a candidate to support in that election even if they don’t in their district’s House election. Research by David Wasserman of the Cook Political Report tracks the Median District Bias using the presidential popular vote and shows a consistent Republican advantage (and Democratic disadvantage) over the last 50 years. The edge has increased from 2%-3% in the 1980s and 90s to nearly 6% in 2016, vindicating liberal concerns of a structural imbalance. 

Explaining the Median District Bias

The Republican Party’s efficient distribution of voters — a result of natural sorting and gerrymandering — is the root of their advantage in the Median District Bias. While Democrats run up big margins in deep blue districts, Republicans spread their votes out among swingier ones. In 2018, Democrats won 195 districts by 10% or more. Republicans won 151 such districts. Democrats had a disproportionate number of voters squeezed into 195 safe districts. While these voters drag the national popular vote leftward, they do nothing to change the median House seat’s margin.

A second possible explanation is voter turnout. If one party disproportionately wins districts with a low turnout, that would lower its popular vote tally without affecting the median district’s margin. The data show the opposite of what we would expect given the Republican advantage in the Median District Bias: Democrats win the districts with the smallest turnouts. In 2018, Democrats won all 30 districts with the fewest votes cast. This stems from the demographics of the Democratic coalition: the party performs better with low-wage, minority, and young people. Democrats win the votes of these low-propensity voters, meaning that they win districts filled with these low-propensity voters and therefore win districts with low voter turnout.

The Seat Bonus Bias

Another measure of House bias is the gap between each party’s share of the national popular vote and their share of seats. This gap is called a “seat bonus.”

In a perfectly proportional system, a party that wins 51% of the popular vote would receive 51% of the seats. The House, though, is decided by 435 individual elections rather than proportional allocation, making such a distribution of seats unlikely. In 2016, Republicans won 51% of the two-party House popular vote (which excludes third party and independent votes) and 55% of seats in the House (241 out 435). The Republican seat bonus, therefore, was 4%.

Figure 1 shows Democratic and Republican seat bonus in the House from 1972 to 2018 using the two-party vote. The 1972 election marked the first full redistricting cycle after the Supreme Court’s “one person one vote” rulings in the 1960s, making it a good starting point for House analyses.

Figure 1: House seat bonus using two-party vote, 1972-2018

SourceBrookings Vital Statistics on Congress; All data in the graph is rounded to the nearest 1%.

The figure shows two eras of Democrats bias (1972 to 1994 and 2006 to 2008) and two of Republicans bias (1996 to 2004 and 2010 to 2016). The 2018 midterms seem to have broken this last era favoring Republicans, but we need future election results to be sure.

These four eras line up with party control of the House. Democrats won majorities from 1972 to 1992 and 2006 to 2008 while Republicans did from 1994 to 2004 and 2010 to 2016. The party that wins the House almost always receives the seat bonus. Of the 24 congressional elections since 1972, only 1994 broke the trend. Over these 24 elections, the winning party got an average seat bonus of 6%. This bonus, however, has decreased from an average of 8% between 1972-1982 to 5% from 2008-2018.

Figure 2 is similar to Figure 1 above, but includes third party and independent votes.

Figure 2: House seat bonus using total vote, 1972-2018

SourceBrookings Vital Statistics on Congress; All data in the graph is rounded to the nearest 1%.

In this graph, the trendlines for both parties are consistently a few percentages higher. When third party votes are included in the national popular vote, both Democrats and Republicans get a bigger seat bonus. The reason for this is clear: third party votes increase the raw number of votes, but rarely translate to real representation in the House.

Democrats and Republicans both benefit from the Seat Bonus Bias when they win control of the House, disrupting claims of a Democratic structural disadvantage. The real penalty is on third parties and independents.

Explaining the Seat Bonus Bias

To explain the seat bonus, we need to know what dynamics boost a party’s share of House seats relative to its share of the national popular vote. Such explanations revolve around overperformance in swing seats. This is because small improvements in close races could push a party over the top to win these districts while barely registering in the national popular vote. Imagine that Democrats got a 3% boost in their 10 closest losses o­f 2018. They would have won each of those districts, increasing their House representation by 2% (10 seats out of 435) while boosting their national popular vote total less than 0.1% (around 40,000 votes out of 61 million): a seat bonus of 2.9%. So, what could cause this kind of overperformance in swing seats?

First up: the incumbency advantage. In years when the House flips, the seat bonus is almost negligible (1994, 2006, 2018). But the following year — once the controlling party has the incumbency advantage in crucial swing districts — that seat bonus grows (1996, 2008, 2012, and maybe 2020). The incumbency advantage in swing seats will help the controlling party hold onto these seats even if its national performance suffers. In 1994, for example, Republicans won 54% of the two-party popular vote and 53% of House seats. The following election, their share of the popular vote fell to 50%, but they held onto 52% of House seats. This drop in the national popular vote (-4%) with a proportionally smaller drop in representation (-1%) translates to a 3% increase in seat bonus. However, the incumbency advantage does not account for every seat bonus. There must be other explanations.

One lies in the sheer number of swing seats, defined here as those won by either party by less than 10%. This range — from +10% Democratic to +10% Republican — covers a scope of 20%. There were 88 such districts in 2018. Election margins on the whole can range from 100% Democratic to 100% Republican, a scope of 200%. Our definition of swing seats accounts for 10% (20%/200%) of all possible results. The 88 swing seats of 2018, though, make up 20% of all 435 House seats. This overrepresentation of competitive districts means that a small increase of a party’s national popular vote could flip a disproportionate number of close races.

Another explanation is the “elasticity” of these swing seats. FiveThirtyEight explains elasticity as “how sensitive [a district] is to changes in the national political environment.” These 88 swing seats of 2018 have a mean elasticity score of 1.03 (and a median of 1.02), meaning that for every 1% change in the national popular vote, these seats will move an average of 1.03% in the same direction. And while this .03% gap may seem trivial, eight seats in 2018 were decided by less than one percent. This amplification in swing seats could push the winning party over the top in competitive races, giving them a seat bonus.

Each of these factors — the incumbency advantage, the overrepresentation of swing seats and elasticity — and more contribute to the Seat Bonus Bias.

Looking ahead to 2020

According to FiveThirtyEight’s aggregator and adjusting to exclude third party and undecided voters, Democrats lead the 2020 generic ballot 53.8% to 46.2%, a 7.6% margin. As I lay out on my personal blog, the generic ballot is pretty good indicator of the national popular vote. A 7.6% lead in the national popular vote would probably push Democrats past the Republicans’ Median District Bias, allowing them to hold onto the House. Democrats would also probably benefit from the Seat Bonus Bias, giving them more than 53.8% of House seats (234 seats). But it is still early. This number is bound to change over the next 14 months.

And remember, the House is decided by 435 single-member districts, not the national popular vote. With single-member districts come natural sorting and gerrymandering that inject bias and unpredictability into the system. Which brings us back to the original questions: does this bias always work against Democrats, giving them a structural disadvantage in the House? The Median District Bias says yes; the Seat Bonus Bias says no. As with everything in politics these days, the answer comes down to the nature of your bias.

Seth Moskowitz is the founder of the elections blog,, which focuses on the U.S. House. He graduated from Emory University in 2017 and specializes in political and non-profit communications. Seth can be reached at or on Twitter @skmoskowitz.