The upcoming Senate map has been on “borrowed time” for Democrats for almost two decades, but a mix of exceptional candidate quality and excellent environments have kept them afloat for quite some time. In 2006, Democrats defeated six of the so-called “Class I” Republicans, flipping the Senate in a wave fueled by the unpopularity of the Iraq War and a number of House Republican scandals. Next, 2012 saw five Democrats elected in states that simultaneously voted for Republican presidential nominee Mitt Romney by double digits. Most recently, in 2018, despite losing incumbents in three red states, Democrats capitalized on a favorable political environment to flip Arizona and Nevada while holding seats in six Trump-won states, including Montana, West Virginia, and Ohio.
Since 2012, though, accelerating polarization has made states’ presidential results much more predictive of outcomes in simultaneous Senate contests. In the 2000 election, voters in 10 states chose a presidential and Senate candidate from two different political parties. By 2016, the winning parties for both offices were the same nationwide – a first in the modern history of the Senate chamber. This phenomenon almost repeated itself in 2020, but moderate Republican Susan Collins pulled off an upset in Maine by outrunning incumbent Republican President Donald Trump by 18 points.
Given this stratification of partisanship, our initial ratings favor the GOP to retake the Senate majority with 51 seats, especially because of the uniquely asymmetric map; Democrats will be defending three Trump-won seats, while the Republicans are not defending any Biden-won seats. But while Democrats face an uphill battle to hold the Senate, we think there’s too much uncertainty to write them off just yet — Republican recruiting issues doomed their campaign to reclaim the Senate in 2022, and there are early indications that this might happen again in 2024.
Key Contests
Republicans are on offense in most of 2024’s key Senate contests. Their easiest target is West Virginia, the reddest state with a Democrat Senator. Senator Joe Manchin, a moderate, won by just 3 points against a weak challenger in 2018, and posted a WAR of D +31. While that score is impressive, it implies that Manchin would still come up short in 2024, given that Trump won the state by 38 and 42 points in his last two elections. Although he hasn’t announced a potential bid for reelection, the Democratic nomination is the Senator’s if he chooses to take it.
While West Virginia is likely too Republican for a controversial recruit to stop the GOP from flipping the seat, Congressman Alex Mooney, a repeated WAR underperformer, is definitely a weaker candidate than the primary frontrunner, Governor Jim Justice. Despite preliminary polls showing Manchin ahead of Mooney, we would consider either Republican a clear general election favorite given the state’s partisan lean.
Manchin last faced presidential-year turnout in 2012, when voters were more likely to split their tickets. Multiple Democratic row officers also held office during this period, but lost due to Trump-era polarization. As such, there is no probable path for any Democrat to win a federal race in West Virginia in 2024; we feel comfortable beginning the race at Safe Republican. If Manchin wins, it would be the single greatest upset in modern electoral history.
Senator Sherrod Brown, the lone statewide-elected Democrat remaining in Ohio, also faces a difficult reelection. To win, he would need two key metrics to fall in his favor. First, Biden would have to reduce Trump’s 2020 margin in Ohio to close the distance to the finish line for Brown, whose D +1.2 WAR is underwhelming considering the financial and environmental advantage he had over his underfunded opponent in 2018.
Second, educational polarization would have to work in Brown’s favor. Since 2016, the opposite has happened. Non-college white voters, a majority of the voters in Ohio, have net Republicans more votes than what Democrats have been able to muster from college-educated voters, especially in the Cincinnati and Columbus suburbs. Brown has historically overperformed among non-college whites and a win in 2024 ultimately depends on his ability to “slow the bleeding” with that demographic.
Adding to Brown’s challenges, is a greater Republican investment in next year’s race — a far cry from their dilapidated 2018 operation. Ticket-splitting will also likely be significantly lower in 2024 than it was in 2018, given that Brown is running for reelection in a presidential year and polarization has only increased since his last run.
It’s too early to tell whether Brown, a modest overperformer, would be able to overcome Ohio’s unfavorable fundamentals with Trump at the top of the ticket. On paper, this is the GOP’s race to lose, but Republicans could increase Brown’s reelection chances if they nominate an underperformer similar to Ohio’s junior Senator, J.D. Vance. We begin this race at Leans Republican.
The third vulnerable Democrat is Montana’s Jon Tester, who has won three hard-fought races over the course of his career. Tester did best in 2018, taking a majority of the vote and posting a D +11 WAR. While the incumbent Democrat is a proven overperformer, his fate will depend most on the quality of his Republican opponent.
At the moment, Congressman Matt Rosendale (R, MT-02) is the frontrunner. Given his 11-point underperformance in his 2018 loss to Tester, though, NRSC Chairman Steve Daines has pushed for former Navy SEAL Tim Sheehy to join the race. A rough primary between Rosendale and Sheehy would likely push the campaign’s tone to the right, giving Tester more of an opportunity to further stress his moderate credentials.
Tester also enjoys positive approval ratings in virtually every public poll of the Montana electorate. Generating crossover support is much easier for popular incumbents, especially those in states with small populations that are prone to ticket-splitting like Montana. Democrats could also offset rural slippage by turning out untapped voters in both Democratic bulwarks like Missoula and Bozeman, and also on Native reservations.
The combination of massive, recent electoral overperformance, higher levels of ticket-splitting, untapped Native votes, and weaker-than-average expected opposition makes Tester less vulnerable than Brown, and especially Manchin, to start.
Fundamentals favor the GOP over the Democrats in Montana, but Tester has come out on top in three difficult races. For now, we are acknowledging the uncertainty in the race with a Tossup rating.
The GOP could also target Biden-won Wisconsin, Michigan, Nevada, and Pennsylvania alongside the previously-mentioned states. Each of these would be a prime target if a Republican is winning the White House, but low candidate quality could jeopardize GOP chances across the board as it did in 2022. In Pennsylvania, which begins at Likely Democratic, a Republican nomination of Doug Mastriano against Senator Bob Casey, a formidable incumbent with a well-established familial brand, could move the seat off the board altogether. The story is somewhat similar in Nevada, where election denier and failed 2022 Secretary of State candidate Jim Marchant seems like a slight early frontrunner for the GOP nomination in this Leans Democratic race.
Prospects in Wisconsin and Michigan look somewhat better for Republicans than they do in Pennsylvania; both states start at Leans Democratic. However, underperforming Republican nominees helped Democrats win gubernatorial races in both states in 2022, and it’s possible that the same dynamic could help elect both Senator Tammy Baldwin and the apparent Democratic nominee and Representative Elissa Slotkin next fall, even if Trump narrowly wins both states. Split Ticket WAR models suggest that both Baldwin and Slotkin are stronger than average, and it will take strong nominees to beat them.
Democrats’ best offensive target is Texas, where controversial Republican Senator Ted Cruz is running for reelection. His likely general election opponent is Dallas Congressman Colin Allred. Overall, Texas has been trending Democratic despite recent Republican gains with Hispanic voters in South Texas. Given that Cruz is a WAR underperformer, we do not expect him to significantly outrun Trump like his colleague John Cornyn did in 2020. At the same time, Texas remains about 10 points to the right of the national popular vote, and an environment similar to 2020’s would likely result in a Cruz re-election. Out of an abundance of caution, we are starting the race at Likely Republican.
Florida presents a similar scenario: a Republican-leaning state with a similarly-embattled incumbent Senator. The state’s recent rightward lurch, however, will likely help entrench Senator Rick Scott to a probable victory. Again, a rating of Likely Republican reflects the proper level of uncertainty for this race.
Arizona is the final state of interest for 2024. Incumbent Senator Kyrsten Sinema, elected as a Democrat six years ago, may run for reelection as an independent. Democratic Congressman Ruben Gallego has already entered the race, which could become the most high-profile three-way contest in over a decade.
In theory, a split liberal vote would reduce Democratic chances in Arizona, like it did in Florida in 2010. But Sinema’s low approval ratings among Democratic voters suggest she may actually draw more votes from independents and moderate Republicans than from Democrats. Her low approval ratings overall make her bid less threatening than that of then-incumbent Florida governor Charlie Crist in 2010. Controversial Republican underperformers from 2022 like Kari Lake and Blake Masters could also prove unelectable in a three-way race, even in a presidential year. We are starting the race at Tossup given the uncertainty this race portends.
Final Thoughts
The story of the 2024 map is likely to come down to the clash between candidate quality and fundamentals. In virtually every scenario in which the GOP nominates generic candidates, they would easily gain several seats, simply due to what fundamentals suggest about the partisan balance of the map. But that hypothetical is not the world we currently live in, and given the sheer number of races lost by the Republicans due to suboptimal candidates of late, we believe that the burden of proof lies on the GOP to prove that they have the discipline, as a party, to nominate candidates who can exploit these openings against a slate of strong Democratic candidates. The Republicans remain favored to flip the chamber in our initial set of ratings, but these gains are far from guaranteed at the moment.