Sussing Out The Senate

Time to take a look at the race for control of the US Senate, and the good news is with just over six weeks to go, Democrats are favored to take back control of the upper chamber.

Democrats are slight favorites to regain control of the Senate, according to the FiveThirtyEight Senate forecast, which launched today. But the map is wide open, with at least a dozen competitive races — none of which are certain pickups for Democrats — including some states where Democrats are playing defense.

In fact, while it’s possible that Democrats will wind up controlling 54 seats or perhaps even more, the most likely outcome is a much more closely divided chamber, including the possibility of a 50/50 split in which control of the Senate would be determined by whether the vice president is Kamala Harris or Mike Pence. (Joe Biden and Harris currently have a 76 percent chance of winning the presidential race, according to our forecast.1)

Our Congressional model (our forecast for House races will be released soon) is largely the same as the version we built in 2018, which was quite accurate in predicting the number of Senate and House seats that each party would win. We’ve made a handful of changes since 2018, most of which were designed to create more consistency with our presidential forecast, including assuming that uncertainty is slightly higher this year because of an increase in mail voting under COVID-19. But these adjustments don’t greatly change the outlook. For a complete list of changes, see our methodology guide.

As in 2018, there are three versions of the model, which build on one another and become increasingly complex:

he Lite version of the model relies as much as possible on polling. In races that don’t have much or any polling, it calculates the candidates’ standing from other races that have been polled.

The Classic version relies on polling but also incorporates “fundamentals” such as fundraising, incumbency and a state’s partisan lean relative to the rest of the country.

Finally, the Deluxe version takes all of the above and adds in expert ratings from The Cook Political Report, Inside Elections and Sabato’s Crystal Ball.

By default, we’re showing you the “Deluxe” version of the model this year. It’s supposed to be the most accurate one and — given everything going on — we’re inclined to cut to the chase. But you can toggle between the versions using the magnifying glass icon at the bottom of the page.

You might want to get in the habit of doing this, too, because there are some fairly large differences between the model versions this year. This reflects the fact that the polling in individual Senate races is generally quite good for Democrats, while other indicators and expert ratings are more equivocal. For instance, the poll-centric Lite version of the model currently gives Democrats a 68 percent chance of winning the Senate, as compared to a 64 percent chance in the Classic version and a 58 percent chance in the Deluxe version.2

So depending on the model, the Dems have a 58-68% chance of controlling the Senate, but the most likely outcome of all three models remains either 50 or 51 seats.  It's not a done deal by any stretch, Dems are going to have to get five seats to offset Doug Jones's near guaranteed loss in Alabama and get to 51, but they have a very good shot at Maine, Colorado, NC and Arizona and getting to 50. Their next best shot is Iowa and Theresa Greenfield upsetting Joni Ernst, followed by Steve Bullock knocking out Steve Daines in Montana, or Jon Ossaof getting lucky in Georgia. Jones is actually next on that list, but he's looking at 27% odds and it gets worse from there for the Dems, even with Jaime Harrison in SC.

We'll see what happens.  The Dems can get to 50, but after that, well...it gets dicey for 51 and beyond.

But if even one of those upsets happen...it's all they need for 51.