When we handicapped our initial Senate ratings, we noted that this cycle might finally be the year that the Class 1 Senate map (which held contests back in 2018, 2012, 2006, and so forth) turns on Democrats. Buoyed by uncharacteristic success in red-leaning states, and aided by a plethora of awful GOP candidates, Democrats managed to keep their caucus a lot larger than their fundamentals would have predicted in previous years.
But there were signs that this luck was running out. Even in 2018, there were a few incumbents who could not escape polarization — the seats in the deep-red states of Missouri, North Dakota, and Indiana all flipped to the GOP, despite strong Democratic incumbents posting overperformances.
This cycle, Republicans need to gain just two seats to win an outright majority. With three red-state seats up for grabs in Montana, West Virginia, and Ohio, the Democratic majority looks more imperiled than ever, especially with the rise in polarization and the presence of Donald Trump on the ballot.
Today, we’re introducing our quantitative Senate model. This model accounts for spending, incumbency, partisanship, polling, and past overperformance to assemble probabilistic estimates of each Senate race. While there are a few differences, this is largely similar to our House model. Our forecast finds Republicans favored in 51 seats, with Democrats favored in 48. In our simulations, Republicans hold the Senate 84 percent of the time. (You can find the model outputs here, or a spreadsheet link here if you prefer that.)
One state (Ohio) remains too close to call, where it is unclear whether long-time incumbent Sherrod Brown can capitalize on his strength and opponent Bernie Moreno’s numerous weaknesses in a state Trump will likely win handily. However, it is important to remember that if results in Montana and West Virginia swing the way of Republicans, and if they can hold serve in Texas and Florida (where the GOP incumbents are heavily favored), then the GOP doesn’t need Ohio to win.
Because of this, we find that Republicans are currently clear favorites to retake the Senate. Joe Manchin’s retirement took R+40 West Virginia out of even hypothetical competitiveness, and we find Montana’s Jon Tester to be an underdog against Tim Sheehy, with public and private polling showing a slim Republican lead. However, the GOP has had less success at widening the electoral battlefield.
Differences in candidate quality in states such as Wisconsin, Arizona, and Nevada mean that even on a night where Donald Trump wins those states at the top of the ticket in the presidential race, the Democratic candidates for the Senate might also comfortably win their races. Most apparent is Arizona, a tossup state where liberal Democratic Rep. Ruben Gallego has opened up a solid lead over Kari Lake, the 2022 gubernatorial candidate now infamous for denying her loss to Katie Hobbs.
Meanwhile, Republican efforts against Senators Tammy Baldwin and Jacky Rosen have failed to dent their clear leads in Wisconsin and Nevada, respectively, as weak candidates with no prior electoral experience and limited local ties continue to falter against well-funded Democratic incumbents. It did not have to be like this — had Republicans picked anyone with a modicum of prior experience and some more credible state ties, these races could have become competitive. However, at the moment, our forecast finds Democrats to have 3:1 odds in these states, despite tossup presidential races in both.
An interesting case of perhaps misallocated priorities is the pair of Senate races in Pennsylvania and Michigan. In Pennsylvania, Republicans have raised roughly $16 million to fund David McCormick against Senator Bob Casey, in what our model currently rates a Likely Democratic race. Casey’s solid polling leads have not budged, and McCormick’s efforts have mostly failed to gain traction; the former hedge fund CEO’s campaign has spent more time hamstrung by carpetbagging accusations than making any headway in the race.
By comparison, Michigan’s Senate race is open, with Democratic representative Elissa Slotkin matching up against former GOP congressman Mike Rogers. Unlike every other swing state GOP challenger this year, Mike Rogers has credible electoral experience. However, he has only raised $5 million, a meager total that is nowhere near saturation point for the state markets, and a figure that Slotkin has comfortably lapped several times over. This, combined with good polling for Slotkin and Kamala Harris, gives Democrats a clear edge in our forecast.
Most Senate commentary this cycle wisely focuses on Democratic defense, as there are no immediate opportunities for Democrats to flip seats from Republicans. The two likeliest seats to become competitive that are currently in the red column are Texas and Florida. Both races feature solidly right-wing Republicans facing off against former Democratic congressmen with solidly liberal voting records. In Texas, Ted Cruz faces Colin Allred, and in Florida, Rick Scott will likely face Debbie Mucarsel-Powell.
Both Allred and Mucarsel-Powell have been relatively quiet, and there is no major effort observed to move the partisan needle. Some of this is no doubt due to a desire to go on offense late, but while our forecast gives them both a puncher’s shot of winning, we still find it unlikely. In a presidential year, when both states are likely to vote for Donald Trump by at least five points (and possibly more), the climb is likely to simply be too steep, even against unpopular Republican incumbents.
Control of the Senate in all likelihood will come down to whoever can win the Montana Senate seat. Currently, Republicans are 75% favorites to flip the seat with businessman and former Navy SEAL Tim Sheehy, with Tester a clear underdog in an R+16 state. Our model gives the incumbent Democratic senator a 25% chance of winning. The race is certainly winnable for Democrats, but it is a tall order — to contextualize this, his odds are actually similar to Colin Allred’s 17% chance of flipping Texas blue.
This scenario illustrates the state of play in the Senate this cycle: Republicans are betting on polarization kicking in to knock out Tester and Brown to deliver a very narrow majority to the GOP in January 2025. This makes sense for a party playing for the majority, but given the balance of the map, one can’t help but think that the party is leaving a lot of opportunities on the board due to self-inflicted wounds and poor recruiting decisions.
If Democrats were not so overextended on this particular Senate map, the candidate quality deltas would likely yield much better results. As it is, it’s a minor miracle that virtually no battleground state’s senate seat is even that competitive at the moment — the only places Democrats are truly at risk of losing seats are in deep-red states. But that is all the GOP needs, and given the decline in ticket-splitting that has hurt red-state Democrats in the past decade, it makes sense to not bet against polarization.
I’m a computer scientist who has an interest in machine learning, politics, and electoral data. I’m a cofounder and partner at Split Ticket and make many kinds of election models. I graduated from UC Berkeley and work as a software & AI engineer. You can contact me at lakshya@splitticket.org
I’m a political analyst here at Split Ticket, where I handle the coverage of our Senate races. I graduated from Yale in 2021 with a degree in Statistics and Data Science. I’m interested in finance, education, and electoral data – and make plenty of models and maps in my free time.