Midterm Election

In the United States, a midterm election occurs every four years at the midpoint of a presidential term. All 435 seats in the House of Representatives, roughly one-third of the 100 Senate seats, 34 or 36 governorships (depending on the cycle), and thousands of state legislative and local offices are contested. The president is not on the ballot, which tends to nationalize the vote into a referendum on the incumbent administration.

Midterms historically favor the party out of power. Since the end of World War II, the president's party has lost House seats in nearly every midterm, with notable exceptions in 1998 (Clinton, during impeachment proceedings) and 2002 (Bush, following the September 11 attacks). Average losses for the president's party run to roughly two dozen House seats, though margins vary widely with presidential approval ratings, economic conditions, and turnout composition.

Turnout in U.S. midterms is consistently lower than in presidential years. In 2018 it reached about 50% of the voting-eligible population — the highest midterm turnout in a century — while 2014 saw turnout near 36%. Because the midterm electorate skews older, whiter, and more partisan than the presidential electorate, small shifts in mobilization can produce large seat swings.

Beyond Congress, midterms shape state-level power: governors and legislatures elected in years ending in 0 typically oversee post-census redistricting, giving midterms outsized influence on the next decade's congressional maps. Ballot initiatives on issues such as Medicaid expansion, abortion access, and minimum wage have also become defining features of recent cycles.

Other presidential systems use the term loosely. In the Philippines, "midterm elections" refer to the legislative and local contests held three years into the president's six-year term. In Argentina and Mexico, midterm legislative elections similarly serve as a check on the sitting executive.

For researchers, midterms are a key data point for measuring presidential popularity, partisan realignment, and the effectiveness of party organizations between presidential contests.