Published March 23, 2018
Most news stories about the midterm elections focus on Republican weaknesses. President Donald Trump’s approval ratings are low, Republicans trail in the generic ballot, and enthusiasm among Democrats seems likely to boost their turnout. Despite these factors, there is one ray of sunshine for the GOP: the U.S. Senate. Both polling and historical analysis suggest Republicans could gain seats there even as the party generally suffers a downturn.
GOP hopes in the Senate rest on the fact that an unusual number of Democrats up for reelection represent states Trump won in 2016. While five come from states that Trump won with less than 50 percent of the vote, the other five come from very strongly Republican places. Trump’s margin in these states ranges from a low of 18.5 percent (Missouri) to a high of 42 percent (West Virginia). In as sharply polarized a political environment as ours, it is extremely difficult for a senator of one party to win enough votes from the other party’s voters to surmount such large deficits.
The very same polls that show Republicans losing nationally bear this out. The Economist/YouGov poll, for example, shows that only 2 percent of 2016 Trump voters and 3 percent of 2016 Hillary Clinton voters intend to vote for a congressional candidate of the opposite party this fall. A February poll from Public Policy Polling shows essentially the same thing: 7 percent of Trump voters and 5 percent of Clinton voters intend to defect in the fall. If you apply those ratios to the Trump share of the vote in the five states mentioned above, Republicans would easily win them all.
The key for Democrats, then, is whether incumbents can run far enough ahead of Hillary Clinton’s vote share to turn the partisan statistics around. This could happen, in theory. We know that incumbents can differentiate themselves from presidential candidates even in today’s environment. Republican Sens. Pat Toomey and Ron Johnson, for example, ran ahead of Trump in winning their states in 2016. The question is whether it is possible for the Democrats to run far enough ahead of their party to win in the deeply red states that are in play this fall.
The available data suggest they probably won’t. One way to measure the ability of an incumbent to outrun a presidential candidate is to divide the incumbent’s share of the vote by that of the last presidential candidate to run in that state. Any total above 100 shows the incumbent outran the presidential candidate. So we could see whether Democrats can overcome deep partisan trends by examining how Democrats have done in the recent past when facing serious Republican challenges and then comparing those efforts with what they need to win this fall.
The results of this analysis are not good for Democrats. Looking at Democratic Senate races in deep red states since 2004, we find that Democrats have ratings ranging from 103 to 126. They do outrun their more liberal presidential candidates, but not by more than 26 percent of that candidate’s total. Clinton, though, did so poorly that the most endangered five Democrats need to outrun the Clinton and Jill Stein vote share by between 29 and 83 percent. Unless they do better than any other Democrat has done in the past 14 years, each candidate looks like a loser.
Democratic partisan enthusiasm could save some of these people, as could Republicans nominating a terrible candidate as they did in some races in 2010 and 2012. But those factors probably won’t save them all. The likelier outcome is that even as Republicans lose House seats and governors’ mansions, they will pick up between one and four net Senate seats in the fall and maintain Senate control. Given the importance many ascribe to the Supreme Court, that is a strong silver lining to what may otherwise be a very cloudy GOP election forecast.