Every two years all 435 House seats and about a third of the Senate are on the ballot (the two chambers). Elections in the middle of a President's term are midterms. Two patterns stand out.
| Pattern | What the record shows (about) |
|---|---|
| The incumbency advantage | House members who run for reelection usually win more than 90 percent of the time; senators somewhat less often |
| The midterm loss | the President's party has lost House seats in nearly every midterm; from 1934 to 2018 the average loss was about 28 House seats and 4 Senate seats |
Why it works
Why do incumbents win so often? Name recognition, a record of service to the district (casework, local projects), easier fundraising, and district lines often drawn to be safe for one party (redistricting). Strong challengers often wait for an open seat. Why does the President's party lose in midterms? Scholars offer several reasons: presidential-year "coattails" fade when the President is not on the ballot, voters dissatisfied with the President are more motivated to vote, and some voters prefer balance between the branches. There are exceptions: the President's party gained House seats in 1934, 1998 and 2002. Senate races are statewide, so they are often more competitive than House races.
Key idea
Most House members who seek reelection win (the incumbency advantage: name recognition, fundraising, district lines); the President's party usually loses seats in midterm elections.
Worked example: Midterm or presidential?
Which of these was a midterm election year: 2016, 2018, 2020?
- Presidential elections fall in years divisible by 4: 2016 and 2020.
- 2018 falls between them.
Answer: 2018.
Worked example: Reading the pattern
A President's party holds 222 House seats before a midterm. Based on the long-run average, about how many might it hold after?
- The average midterm loss from 1934 to 2018 was about 28 seats.
- 222 − 28 = 194.
Answer: About 194, though any one election can differ a lot.
Common mistake
Thinking Congress turns over a lot each election. Reelection rates for House incumbents who run have usually been above 90 percent; most change comes from open seats, retirements and occasional "wave" elections. Check: was the incumbent running?