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Wave elections (1918-2016)/Limitations
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House waves • Senate waves • Gubernatorial waves • State legislative waves |
Competitiveness in State Legislatures |
June 19, 2018
By: Rob Oldham and Jacob Smith
This page reviews the limitations of the study for each election type.
U.S. House limitations
Our analysis does not account for redistricting. Political parties and incumbent lawmakers can use the redistricting process to redraw congressional boundaries into districts that favor their party under normal electoral conditions.
Because of this, it might be difficult to compare the results of elections that did not occur under the same district lines. For example, Republicans controlled the redistricting process in states holding 40 percent of U.S. House seats following the 2010 elections. Democrats controlled the redistricting process in states holding 10 percent of U.S. House seats.[1][2] If Republicans redrew the lines to benefit their candidates, then it might lower the threshold for a Democratic wave because seats will be more difficult to win than under Democratic-controlled redistricting.
According to elections analyst David Wasserman, the 2018 House map's bias toward Republicans is at its highest level since at least 1920. In addition to redistricting, he cites the differing geographical distributions of Democratic and Republican voters (i.e., Democrats concentrating in dense urban districts) as a reason for this bias.[3]
Because of the difficulties that redistricting presents, a better way of calculating a wave might be looking at total shifts in the vote margins rather than the seats a party wins or loses. Visit our section on the debate surrounding wave elections to learn more about how other experts have thought about House waves.
U.S. Senate limitations
Only one-third of the U.S. Senate (33 or 34 seats in the present day) is up for election every two years. A party's fortunes are often dependent on whether the seats up for election that year are pick-up opportunities or not. In contrast, the same 435 seats are up in the U.S. House every two years, meaning they are not affected by a changing electoral map and staggered terms.
For example, the political environment surrounding the 2018 elections will likely favor Democrats and give their candidates a boost in many elections. But they are defending 25 of the 33 Senate seats up for election, and 10 of those seats are in states Donald Trump won in 2016. This could limit their ability to make significant gains.[4]
A favorable electoral map for the U.S. Senate (such as the 2018 map for Republicans) can often lead to the presidential party making gains even it if loses seats in the U.S. House and state capitols. Wasserman says that the 2018 Senate map, like the House map, is more biased toward one party than at any point since at least 1920. He cites recent Republican gains in smaller states—which have the same two-seat representation in the body as large Democratic-leaning states like California and New York—as the reason.[3]
Because of the staggered election schedule and the fact that surges in partisan energy might not align with a favorable map, determining what constitutes a wave for Senate elections was the most difficult of the election groups.
Gubernatorial limitations
The number of gubernatorial seats up each year has changed over time as more states have shifted from two-year terms to four-year terms and scheduled elections during midterms rather than presidential elections. The changing number of governorships makes it difficult to identify wave elections because years with more elections have a greater potential for seat losses than years with fewer elections. For example, from 1922 to 1946 there were 33 to 36 governorships up every two years, making comparisons relatively simple. However, from 1980 to 2016 36 governorships were up in midterm elections and 11 to 13 were up in presidential elections. Like U.S. Senate elections, the presidential party's performance is dependent on whether the seats up for election in a given year are pick-up opportunities or not.
The changing lengths of gubernatorial terms over time impede our ability to compare electoral turnover directly. It could be true that re-election rates for four-year term governors and two-year term governors differ. For example, the incumbents running in the 2010 midterms, most of whom had four-year terms, could possibly have had an advantage over the two-year term incumbents running in the 1930 midterms due to longer tenures in office. Accordingly, it might not be fair to compare the 1930 and 2010 midterms if the incumbents had different prospects for re-election. Currently, only New Hampshire and Vermont use two-year terms for governors.
The rise of gubernatorial term limits in the mid- to late 20th century also complicates a direct comparison of gubernatorial elections. From 1950 to 2005, the number of states with unlimited gubernatorial terms decreased from 29 to 12. According to Dr. Gerald Benjamin of SUNY New Paltz in 2005, governors without term limits were more likely to be re-elected because they "dominate news coverage," "become established in the public mind," "use their political advantage in filling jobs and spending money," and "have access to talented people and big political contributors." Without these incumbency advantages, it is possible that turnover among governors, and, thus, their political party, would increase regardless of the backlash against the president's party.[5]
State legislative limitations
See our data explanation section to see which states we used in this analysis and how we handled different term lengths and odd-year elections.
Like the U.S. House, state legislative lines are usually changed once every 10 years during redistricting. That makes it difficult to compare elections that occurred under new district boundaries.
Similar to gubernatorial races, 15 state legislatures have term-limits. Most states with term-limits adopted them in the 1990s and put them into effect in the early 2000s. They could complicate a comparison between elections in the 2000s and earlier elections where term-limits were not in place and, thus, incumbent turnover could have been lower.
Click here to read the report as one page.
Click here to read or download the report as a PDF.
Footnotes
- ↑ The other 50 percent of U.S. House seats were in states under divided government or where courts were responsible for drawing boundaries.
- ↑ New York Times, "How Maps Helped Republicans Keep an Edge in the House," December 14, 2012
- ↑ 3.0 3.1 FiveThirtyEight, "The Congressional Map Has A Record-Setting Bias Against Democrats," August 7, 2017
- ↑ Vox, "Democrats’ prospects in the 2018 midterm elections, explained," November 8, 2017
- ↑ New York Times, "Eight Is Enough," December 5, 2005
