Republican Senators Have 70% Chance of Keeping Control o/t Senate.
NATE SILVER, FIVE THIRTY EIGHT
Our congressional forecasts reflect a blend of several different methods of prediction. But for the most part, those methods tell a fairly consistent story. In the House, for instance, district-by-district polls, the generic congressional ballot and historical trends in midterm elections all point toward Democrats winning the national popular vote by somewhere in the range of 8 to 10 percentage points, which would very probably be enough for them to take control of the chamber.1 So do what we call the “fundamentals,” non-polling indicators that have empirically been useful predictors of races for Congress, such as fundraising totals, past margins of victory and several factors related to incumbency.2
Likewise in the Senate, the different versions of our model, which blend these methods together in different ways, tell a similar overall story to one another. It’s a reasonably happy story for Republicans because the Senate map, which consists overwhelmingly of Democratic-held seats, is highly favorable for the GOP this cycle. The polling-driven Lite version of our Senate forecast has the GOP finishing with 51.3 Senate seats and having about a 5 in 7 chance (more precisely, 71 percent) of keeping control of the chamber.3 The Classic version, which incorporates fundamentals, has them with 50.8 seats and about a 2 in 3 chance (68 percent) of maintaining control instead.4 If you go down to the decimal point, the Classic forecast is ever-so-slightly better for Democrats than the Lite forecast — which implies that the fundamentals are ever-so-slightly better for them than polls — but it isn’t a big overall difference.
The word “overall” is doing a lot of work in the previous sentence, however, because while the top-line prognosis on who might control the Senate is similar in all three versions of our model, the forecasts differ quite a bit from race to race. In particular:
- The fundamentals are more bullish than polls for Democrats in several states with Democratic incumbents — most importantly, in Florida, Missouri and North Dakota.
- But fundamentals are more bearish for Democrats in two important open-seat races: Tennessee and the Mississippi special election.
- Polls and fundamentals are fairly consistent with one another in states with Republican incumbents — including in Texas, where fundamentals support the notion of a competitive race between Sen. Ted Cruz and Rep. Beto O’Rourke.
In this article, I’m going to focus on the first category only: races featuring Democratic incumbents. We’ll cover the other two categories in an upcoming piece.
NATE SILVER, FIVE THIRTYEIGHT