And an explanation:
Though political scientists long have noted the midterm dropoff, they don’t agree on precisely what it means. In an influential 1987 article, James E. Campbell theorized that “the surge of interest and information in presidential elections” typically works to the advantage of one party or the other; that party’s partisans become more likely to vote, while those of the disadvantaged party are more likely to stay home during presidential elections. Independents, “lacking a standing partisan commitment…should divide disproportionately in favor of the advantaged party.” Midterm elections lack that “wow” factor, according to Campbell, and turnout among both partisans and independents return to more normal levels and patterns.
A recent paper by Brown University researcher Brian Knight seeks to evaluate that surge-and-decline theory, as well as two competing explanations of why the president’s party nearly always loses seats at the midterms: a “presidential penalty,” or general preference among midterm voters for expressing dissatisfaction with the president’s performance or ensuring that his party doesn’t control all the levers of government, and recurring shifts in voter ideology between presidential and midterm elections. Knight concluded that while all three factors contribute to what he calls the “midterm gap,” the presidential penalty has the most impact.
