In Defying the Odds, we discuss congressional elections as well as the presidential race.
PS: Political Science and Politics Volume 51, Special Issue S1 (Forecasting the 2018 US Midterm Elections) October 2018 , pp. 1-3 Introduction: Forecasting the 2018 US Midterm Elections
PS: Political Science and Politics Volume 51, Special Issue S1 (Forecasting the 2018 US Midterm Elections) October 2018 , pp. 1-3 Introduction: Forecasting the 2018 US Midterm Elections
With a broad background of midterm history, congressional arithmetic, and the current political climate established, we can now turn to the more systematic estimates of how these factors are likely to come together in this year’s midterm. What follows are four independent congressional forecasts and one state legislative forecast that inform us about what we should expect to come out of this election. Table 1 presents a summary of these congressional forecasts. Although there are differences among them, two points are common. 2018 is likely to be a very good year for the Democrats in the House of Representatives. In fact, all four forecasts expect a Democratic House majority. In the Senate, Republicans are likely to hold their own and perhaps pick up a seat or two. So, on to the forecasts.
Table 1 Summary of the 2018 Midterm Congressional Election Forecasts
Furthermore, the president’s party tends to do worse in the House popular vote than the president does in his approval rating. On average in midterms since 1946, the president has had a +11.3 percentage point net approval rating as of Election Day, but the president’s party has lost the popular vote for the House by 4.9 percentage points. That gap is partly explained by voters’ tendency to seek a balance of political power even if they like the president — something that may be especially relevant this year because, when voters voted Republican for Congress in 2016, most of them expected Hillary Clinton to be president. Republican candidates for the House won voters who disliked both Clinton and Trump by 30 percentage points in 2016. If, hypothetically, Democrats won that group of voters by 30 percentage points instead this year, they’d win the popular vote by around 10 percentage points, not far from where most generic ballot polls have the race.
There still is some relationship between a president’s approval rating and his party’s midterm performance. But even at Trump’s slightly improved values, it isn’t a relationship that bodes well for the GOP. The data in the chart below, for example, would imply roughly a 10-point popular vote loss for the GOP given Trump’s current approval rating
