Double Bunked Races in the U.S. House of Representatives



Double-bunked races (DBRs) are a rare type of election for the United States House of Representatives in which two incumbent members compete for the same seat following redistricting. Due to the rarity of these elections, DBRs remain widely undiscussed among political scientists. This research examines several variables distinctly observable in DBRs and assesses their impact on electoral outcomes. This paper’s findings indicate that higher campaign spending and ideological positions appropriate for a district’s partisan leaning correlates with greater electoral performance, while a representative’s legislative prolificity correlates with poorer electoral performance. Length of incumbency, conversely, has no correlation with electoral outcome.


Following the decennial United States Census, Congressional district boundaries are redrawn in a process known as ‘redistricting’1. Occasionally, redistricting may result in two incumbent members of the House of Representatives being drawn into the same district, and sometimes, instead of choosing to run elsewhere or retire, both incumbents will choose to run for re-election in the same district. This paper will refer to such phenomenon as a “double-bunked race,” or a DBR. This type of race is rather rare, only occurring twenty-two times between 2012 and 20222.

Certain DBRs – particularly those featuring incumbents with high name recognition – have received some attention from pundits, especially those seeking to use them as a litmus test for ideologically-opposed factions within a party3. However, DBRs remains largely undiscussed among political scientists, and no statistical explorations of the phenomenon exist.

DBRs are often messy, costly endeavors, with two incumbent members of Congress using all available resources against their colleague. Accordingly, DBRs tend to consume significant resources and funds; in the 2012 race for California’s 30th District, for example, Democrats Brad Sherman and Howard Berman spent a combined $12 million on their campaigns, compared to an average combined expenditure of $2.3 million per race in other House districts that cycle45.

Incumbents are less likely to run for reelection if they believe they have a significant chance of losing their race6. Thus, one can assume that incumbents typically only choose to undertake the uncomfortable task of running against their colleague in a DBR if they believe they believe they will be able to defeat their opponent. Due to the lack of empirical data on the subject, however, it can be difficult to determine which incumbent holds an advantage in a DBR. Improved clarity could help mitigate the chaos and costs associated with DBRs and perhaps even prevent them from occurring in future.

Furthermore, DBRs can serve as a critical case study in the phenomenon known as incumbency advantage, in which incumbent members of Congress hold a significant edge over challengers when running for reelection7. However, political scientists disagree upon which specific features of incumbency cause or enhance this advantage8. DBRs provide an opportunity to better understand the specific characteristics of incumbency which provide an advantage to officeholders.

This paper conducts an observational study of the determinants of victory in DBRs. The variables examined primarily consist of those affected by both candidates’ incumbent status, such as length of incumbency, ideological position, and legislative prolificity; this paper also examines the impact of campaign spending on outcome in DBRs.


This research examines eighteen different DBRs that took place between 2012 and 2022: eleven in 2012, six in 2022, as well as one in 2016 that took place in North Carolina following court-ordered redistricting due to racial gerrymandering29. Though twenty-two DBRs occurred in this timespan, four were between incumbents of opposite parties. Because races involving candidates of opposite parties are more heavily influenced by a district’s partisan leaning, other variables may be affected; thus, they are excluded from this study.

To research these races, multiple sources were aggregated to collect data on each examined DBR variable. Records from the Federal Election Commission (FEC) were employed to document campaign expenditures10. To quantify and record incumbent ideology and voting patterns, this paper uses Voteview, an extensive database of Congressional voting records. This database, maintained by the political science department at the University of California Los Angeles, provides scores for each representative’s ideology regarding social and economic issues in each session of Congress11. To record the partisan leaning of Congressional districts, the Cook Political Report’s Partisan Voting Index (PVI) was utilized. The Cook PVI measures how each district votes relative to the rest of the nation12.

Finally, Congressional records are used to determine an incumbent’s number of bill co-sponsorships in the session of Congress immediately preceding a DBR13. Using data compiled from these sources, models were generated using R to compare each examined race using the discussed variables in order to draw conclusions about their impact in DBRs.


Campaign spending tends to be among the strongest determinants of election outcome in the U.S. House of Representatives14. To find whether this is consistent in DBRs, a linear regression was generated in R to determine the correlation between percent difference in spending and vote share (i.e., Candidate A spent X% of what Candidate B spent and received Y% of B’s vote percentage). This measures campaign spending holistically, expressing a campaign’s spending and received vote share as it relates to their opponent’s. This regression shows a strong positive correlation between spending and vote-share, indicating that campaign spending still plays a distinctive role in determining electoral outcome in DBRs (Fig. 1).

Figure 1| A linear regression of vote share on campaign spending.

Though incumbency advantage has been established as a prevalent determinant of elections in the United States, political scientists still debate whether an incumbent’s seniority impacts reelection. McKelvey and Riezman (1992) argue that the benefits associated with seniority do help incumbents secure reelection, while Ansolabehere and Pettigrew (2014) claim that incumbent tenure plays little role in gaining support among constituents15,16.If DBRs are to be considered a case study in this debate, the data seems to definitively side with Ansolabehere and Pettigrew: in a cross-tabulation of thirty DBR candidates zero correlation was found (Table 1).

Table 1| Tenure Length vs. Victory Cross-Tabulation

Most DBRs between incumbents of the same party take place during primary elections, meaning that the upcoming general election plays a role in primary voter behavior – especially in competitive districts – as voters are more likely to consider “electability,” or electoral viability in a general election, as a factor. Extremist candidates who win primary elections for the U.S. House face, on average, a 9-13 percentage point decrease in vote share in the general election relative to a more moderate candidate17. Thus, while primary voters in “safe” districts typically vote according to their own ideological position, primary voters in competitive districts may choose to vote strategically, sometimes choosing a more moderate candidate to better their party’s chances in the general election. However, candidate ideology and “electability” can be difficult to quantitatively measure, especially when dealing with candidates who lack a legislative voting record18. However, DBRs provide a rare opportunity in which both candidates have voting records that can be directly compared. Voteview records each Congressperson’s ideological percentile relative to the rest of their party in each session of Congress (with low percentiles indicating moderacy and high percentiles extremism)11. Table II includes these measurements for each candidate as well as the Cook PVI score for their districts.

Table 2| District Partisan leaning and Candidate Ideology Percentile Comparison

Among the eight DBRs that took place in competitive districts (considered to be districts with PVI leanings of 10 points or less), the more moderate candidate won five times, while the more extreme candidate won only twice (since the candidates in the IL-06 race were ideologically separated by less than 5 points, they are not considered here)19. However, among the races in non-competitive districts (that is, races in districts with PVI leanings over 20 points), the more moderate candidate loses a remarkable 5 out of 6 times. This may be because, due to a reduced risk of losing in a general election, a party’s base feels less obliged to vote “strategically” in a primary for a more “electable” candidate, instead choosing a candidate with whom they feel more ideologically aligned.

Finally, a box-and-whisker plot generated using R demonstrates a negative correlation between an incumbent’s bill co-sponsorships in the prior session of Congress and candidate victory (Fig. 2). Though this may sound counterintuitive, one could observe it as a simple product of American political culture. A survey in the 2016 Cooperative Congressional Election Study (CCES) found that most American voters are unaware of the effectiveness of their representatives as lawmakers and determined that “highly effective” lawmakers perform more poorly in their runs for reelection than average or even ineffective lawmakers20. If voters are not paying attention to a representative’s legislative productivity, then lawmakers are wasting their time (electorally speaking) by writing and sponsoring legislation instead of campaigning. Meanwhile, less legislatively active representatives have more time to campaign and garner up donors and supporters.

Though more research would be needed to ascertain the validity of this theory, it is possible that increased legislative activity can directly correlate with reduced campaign activity, which may damage an incumbent’s electoral performance, especially in DBRs.

Figure 2 | A box-and-whisker plot comparing prolificity of legislation sponsorship and electoral outcome.


Ultimately, this data demonstrates that the role played by campaign spending in other elections also apply in DBRs. This data also suggests that in DBRs, primary electorates prefer ideologically moderate candidates in competitive districts, yet prefer ideologically extreme candidates in safe districts. Length of tenure, however, bears no correlation with election outcome in DBRs, and bill sponsorships hold a negative relationship with electoral outcomes, possibly due to lost time for campaigning and fundraising. Conclusively, this paper provides important insight into DBRs and the determinants of their outcomes – insight that has not yet been established in the academic field. Not only does this research provide a new empirical understanding of this rare phenomenon, but it also provides an interesting case study in primary voter behavior as well incumbency advantage – two far more frequently-discussed topics in political science and electoral politics.

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