The term wave election is frequently used to describe an election cycle in which one party makes significant electoral gains. As is often the case with midterms, pundits have speculated about whether or not this year's elections will amount to a wave election.
How many offices need to change party control, though, for an election to be a wave election?
According to our 2018 study, examining the results of 50 election cycles from 1918 to 2016, a wave election occurs when a party:
- Gains seven U.S. Senate seats
- Gains 48 U.S. House seats
- Gains seven gubernatorial offices
- Gains 494 state legislative seats
The definition is based on the results of the 20% of elections in that period that resulted in the greatest seat swings against the president's party.
A 2026 wave election for each office type, then, would result in Democrats holding:
- Fifty-four U.S. Senate seats
- Two hundred sixty-two U.S. House seats
- Thirty-one gubernatorial offices
- Three thousand seven hundred thirty-two state legislative seats
Using these definitions, the most recent wave election for U.S. Senate was in 2014, when Republicans gained nine Democratic-held seats. The most recent for U.S. House and state legislatures was in 2010, when Republicans won 63 Democratic-held U.S. House seats and 702 Democratic-held state legislative seats. The most recent wave election for governors was in 2018, when Democrats gained seven offices.
The most recent wave years for Democrats were 1974 (48 House seats and 695 state legislative seats), 2008 (eight Senate seats), and 2018 (seven gubernatorial offices).
The number of times the president's party has gained seats in a midterm election
While wave elections are often thought of as in opposition to the president's party, the president's party has gained seats in historical midterm years. In midterm election years since 1918, the president’s party gained seats in the U.S. House once and in the U.S. Senate five times. The president’s party gained gubernatorial offices four times and gained seats in state legislatures once.
Here’s a breakdown of the presidential party’s gains in each of those years by office:
U.S. House: In 1934, Democrats gained nine seats in the U.S. House during President Franklin D. Roosevelt’s (D) first midterm in office.
U.S. Senate:
- In 1934, Democrats gained 10 seats during Franklin D. Roosevelt’s first midterm
- In 1962, Democrats gained four seats during President John F. Kennedy’s (D) first midterm
- In 1970, Republicans gained three seats during President Richard Nixon’s (R) first midterm
- In 1982, Republicans gained two seats during President Ronald Reagan’s (R) first midterm
- In 2018, Republicans gained two seats during President Donald Trump’s (R) first midterm
Governors:
- In 1926, Republicans gained seven governorships during President Calvin Coolidge’s (R) first midterm
- In 1934, Democrats gained one governorship during Franklin D. Roosevelt's first midterm
- In 1986, Republicans gained eight governorships during Reagan’s second midterm
- In 2022, Democrats gained two governorships during President Joe Biden’s (D) midterm
State legislatures: In 2002, Republicans gained 110 state legislative seats during President George W. Bush’s (R) first midterm
To read more about wave elections, click here.