Disclaimer. Don't rely on these old notes in lieu of reading the literature, but they can jog your memory. As a grad student long ago, my peers and I collaborated to write and exchange summaries of political science research. I posted them to a wiki-style website. "Wikisum" is now dead but archived here. I cannot vouch for these notes' accuracy, nor can I say who wrote them.
Kernell. 1977. Presidential popularity and negative voting: An alternative explanation of the midterm Congressiona. APSR 71: 44-66.
The literature postulates a "surge and decline" effect: During presidential years, candidates rally lots of people to the polls. Candidate personalities clash, making the election interesting. Lots of independents come out and create presidential coattails. Midterm elections, on the other hand, feature poorly-known candidates and less interesting issues. Thus, even if the Republicans enjoy a surge of support (from lots of independent voters) in a presidential year, fewer people turn out and fewer people defect in off years.
(Background: Miller and Stokes knew that the president's party almost always loses seats in midterm elections. Their surge and decline theory was nice, but didn't work. Also, it didn't explain 'how many' seats the president's party should lose.)
Midterm elections are a referendum on the incumbent president. People vote for or against the president's party. Negative voting is stronger (as an effect on Congressional voting) in midterm elections than presidential elections for two reasons.
Research by the same authors
Research on similar subjects