The Senate map for Democrats this fall is daunting.
Republicans are only defending nine Senate seats up for reelection, while Democrats are defending 26 seats. Moreover, 10 of the Democratic-held seats are in states Donald Trump won in 2016 and five are in states he won by about 20 points or more.
Yet, a look at the early polling data suggests that the map may be somewhat misleading. No, Democrats are not favored to take back the Senate. But they are significantly outperforming the 2016 presidential lean in the 2018 Senate races significantly. That gives them a non-nominal chance at winning control.
Since January, 23 of the 35 Senate races in 2018 have been polled. Not all of these polls are the highest quality, but polls not conducted on behalf of the parties or its candidates tell a pretty similar story across the races.
When you compare each race’s average with the 2016 presidential baseline (i.e. how well Hillary Clinton did in the state relative to how she did nationally), Democrats are outperforming in 22 of the 23 races.
In fact, only in Utah (where Mitt Romney is running and in which Trump greatly underperformed the usual Republican performance) are Democrats underperforming the 2016 baseline.
But it’s not just that Democrats are outperforming the presidential lean in so many contests, it’s that they’re outperforming by a lot. On average, they’re doing 14 percentage points better. That average is not being greatly skewed by outliers either. In the median race, Democrats are doing 12 points better than the presidential baseline.
Democrats are also, in the very limited polling, doing much better than the presidential baseline in the states where they need to outperform the most. That is, the states where there are Democratic senators and that went heavily for Trump. This includes states such as North Dakota and West Virginia. Now some of the polling available in those states isn’t of the highest quality, so I wouldn’t read too much into the exact numbers. But the polling does indicate that Democrats are outperforming the partisan baseline in them by over 35 percentage points.
A big reason Democrats are doing so much better than you might expect than the 2016 presidential baseline is that there seems to be a huge incumbent bonus in these races. The 16 incumbent Democrats in our dataset are doing on average 18 points better than the 2016 presidential lean of the state. In non-Democratic incumbent races, Democrats are only doing on average 5 points better than the 2016 presidential baseline.
A large incumbent effect in November would be welcome news for Democrats. Senate Democrats have a lot more incumbents running than Republicans, and many of them are running in red states. Moreover, it suggests that the decline in the incumbent advantage in Senate elections seen during the presidency of Barack Obama may not hold up after it. That’s key not just in 2018 but in the future as well. More states lean Republican than Democratic, and each state has an equal number of senators no matter their population. A larger incumbent effect could help red state Democratic senators hold onto seats
Still, it’s early in the 2018 cycle. Races can shift. In 2016, the trend was for Senate races to revert to the presidential lean of the state they were being held in, even after controlling for the early polling.
Yet, it’s important to point out that Democrats are outperforming the presidential baseline in the average race in 2018 much more so than in any cycle in recent history.
Of all the cycles since 2006, the one that looks most like the 2018 so far is 2008. In an average of January to June 2008 polling, Democratic candidates for Senate were outperforming the presidential baseline by an average of 8 points. That pretty much matched their eventual overperformance of 9 points.
If Democrats continue to outperform the presidential baseline in 2018 by 14 points, it would be an improvement on how they did among this class of senators in both 2006 and 2012. In 2006 and 2012, they ended up doing 10 and 9 points better than the presidential lean.
Of course, an average 14 point overperformance may not be enough to get Democrats to a majority given how many red-state Democrats are defending their seats. It will all depend how the vote is spread out over the different Senate contests. A 14-point swing for the presidential baseline would, as the polling indicates, keep Democrats in the game for a chance at a Senate majority.