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The 2014 midterm election fundamentals (in 4 graphs)

The president’s party tends to lose seats in midterm elections. Period.  The graph above is for the House but the same applies to the Senate.  The logic of midterm loss is laid out nicely in this paper by Robert Erikson.  Part of the story is that the president isn’t on the ballot, and he often supplies coattails for congressional candidates to ride on.  Part of the story is that the electorate may react against the ideological direction of the president’s party–as it has since Obama took office–and seeks to elect candidates from the other party.  In any case, the “midterm penalty” is important.  In elections from 1980-2012, we estimate that this penalty is 3 points of vote share.

We noted nine months ago that taking account of these fundamentals made the Republicans favored to take the Senate.  The quality of the candidates that the GOP has recruited only increased their odds of winning.  In fact, when we debuted Election Lab on May 5, we estimated at that point that the GOP had a 77 percent chance of winning and was predicted to win 53 seats.  We predict 53 seats again today.  The only change is that Michigan and Colorado are flipped relative to that earlier forecast.

And so this leaves us with the last graph, courtesy of Vox.  Although the forecasting models differ in how certain they are in a GOP Senate majority, they see a very similar picture in terms of the most likely outcome: