What’s On the 2024 Ballot #1: U.S. Senate Races
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This series of posts covers various marquee offices holding elections this year by office type: U.S. Senate, U.S. House, governors, etc. Each post will include an overview of the office itself, some historical data when appropriate, what election forecasters have to say (if applicable), and key races to watch out for.
First up is the U.S. Senate, where which party gets the majority is very much at stake.
An Overview of the U.S. Senate
The U.S. Senate has 100 total seats, with members holding six-year terms. Only a third of them — give or take a seat or two — are up for election every two years. With the partisan divide in the U.S. Senate so close — there are 49 Republicans, 48 Democrats, and three independents that caucus with the Democrats — elections for the chamber are even more important.
This year, Democrats are very much on defense, having to defend 21 seats— along with the 3 independent-held seats whose incumbents caucus with the Democrats — while Republicans only have 11 seats to hold onto. (Nebraska has an open seat right now that’s up for a special election — previously held by Republican Ben Sasse, who resigned in 2023 to become the president of the University of Florida — along with its regularly scheduled election for Republican Pete Ricketts’ seat.)
Recent Historical Elections for the U.S. Senate
One of the most reliable predictors of what is going to happen in an upcoming election for a given office is what has happened in previous elections for said office. There is a bit of trickiness involved, however, when using this gauge for the U.S. Senate.
- Having only a third of seats up for election means that different groups of states are having elections. There are greatly varying political contexts for each of those states, so having one batch of U.S. Senate seats isn’t going to be a 1:1 comparison for the next batch two years later. (Some states having U.S. Senate elections in 2024, however, will be having them for their other respective U.S. Senate seats in 2026.)
- Since U.S. Senate elections are staggered (meaning only some seats are up for election in a given year and other seats are up for election in a different year), they happen in both midterm and presidential elections. However, you have to be careful with comparisons between a midterm and presidential election. They have much different turnout rates and different kinds of voters coming to vote. Those who vote in midterm years are very likely to vote in presidential years, but many presidential voters don’t participate in midterms.
All that said, we’ll first take a look at U.S. Senate elections in the past three presidential elections since the years are more comparable, though the seats that were up in 2016 and 2020 were different than this year’s. We’ll also look at the last time this specific batch of U.S. Senate seats were up for election, which was the 2018 election. Though the seats were the same (with the exception of Nebraska’s special election this year), it was a midterm, so it will see a different level of turnout this year than in 2018.
First, here are the U.S. Senate election results for the last three presidential election years. The data comes from Ballotpedia’s election results for the 2012, 2016, and 2020 elections. Presidential elections in recent memory have usually been kind to the winning presidential candidate’s party.
You can see from above that the last three presidential elections have been rough on Republican U.S. Senators. They had a lot of seats to defend in 2016 and 2020 and not many opportunities to pick up other seats, making it difficult for the GOP to not have a net loss of seats. They still managed to maintain a majority in 2016, but lost it in 2020 by the thinnest of margins. (While there were 50 Republicans, the two independents caucused with the 48 Democrats and the vice president is the tie-breaking vote. In this case, that was Democrat Kamala Harris since Joe Biden won the presidential election, and thus the Democratic Party was considered the majority.)
Yet even in 2012, when Democrats had a lot more to defend, Republicans still lost a couple of seats. They were already the minority in the U.S. Senate prior to the election, and the 2012 election expanded Democrats’ lead in the chamber. Cook and Sabato’s race ratings for the U.S. Senate that year did not think highly of most Republicans’ chances in the leadup to the election, and the results bore that out.
Now, what if we look at it by how the seats up for election in 2024 fared in previous elections? U.S. Senate seats are broken up into Class I, Class II, and Class III to signify which seats are regularly scheduled for election at the same time (this does not count special elections, which are inherently not a regular schedule). This year, it’s the Class I seats, which were up for election in 2012 and 2018 as well. The data for the 2018 election also comes from Ballotpedia.
As in 2024, the 2012 and 2018 U.S. Senate elections saw at least 21 Democrats, and at least two independents who caucus with the Democrats, have to defend their seats. (Kyrsten Sinema just recently switched from Democrat to independent, but she is not running for reelection.) We already talked about 2012 above, but 2018 was rough on Democrats. They had even more seats to defend in 2018 than they do this year, and the Republicans expanded their majority in the U.S. Senate — a somewhat unusual occurrence for a sitting president’s party (in that case, Donald Trump).
So, if you look at it through the lens of previous presidential elections, it mostly bodes well for Biden and the Democratic Party. Republicans have lost seats in the last three such elections. If you look at it through the lens of previous elections for this specific set of seats (Class I), it becomes more of a mixed bag, perhaps even slightly favoring Trump.
What Do Election Forecasters Have to Say?
For predictions, we will examine several major election handicappers. Arguably the three most well-known ones are The Cook Political Report, Larry Sabato’s Crystal Ball, and Inside Elections with Nathan Gonzales. Other forecasters we will look at are CNalysis and Split Ticket.
Each forecaster has their own internal criteria for how they rate elections, so they won’t fully agree, but you won’t see a whole lot of deviation from each other. They don’t all have the same terminology either. For example, Cook, Inside, and CNalysis use the term “Solid” while Sabato and Split Ticket use the term “Safe.”
For the most part, these forecasters have seven levels of ranking. But Inside Elections and CNalysis use more than that. So, for those rankings, I’m going to lump their “Tilt D/R” elections with toss-ups (though I will note the number of “Tilt” elections separately with an asterisk). CNalysis also has a “Very Likely” ranking, which I will group with “Likely” rankings in the same category (and note separately with an asterisk). The term “Toss-up” is used across the board but we will rename that, too.
Therefore, for easy comparison, we are going to rename their categories so we can lump them together. It isn’t a perfect system, but this is simply meant to make it easier for readers to put each forecaster’s ratings side-by-side. Below is the terminology I will use and which rankings from each forecaster correspond to said terminology.
Below is how many seats each of these forecasters rates by level. Sabato also has separate ratings for the independent-held seats, but since the occupants caucus with Democrats, I’m going to integrate his ratings for them into the Democratic ratings.
From the get-go, what stands out most is the number of seats that are considered to be definitely Democratic or Republican (Level 3). This isn’t uncommon: A lot of contests in general are a foregone conclusion as to which party will win it. There is, unfortunately, a lack of competitiveness in many races. For example, you can pretty much guarantee that Democrats will win the U.S. Senate seat in California and that Republicans will win the U.S. Senate seat in Wyoming, regardless of who their candidates are.
The chart also shows — partly as a function of how many Democratic seats are up for election as opposed to Republican seats — the number of pick-up opportunities for Republicans. The Level 0 and Level 1 seats are all presently held by Democrats. All of the seats currently held by Republicans are seen as quite likely to stay with their party (the exception being that CNalysis sees Texas as only a Level 1 rating).
Further demonstrating this is the following chart, which shows which races’ ratings are fully agreed upon (e.g. State A is seen as a Level 2 rating by all five forecasters). The rows indicate which party currently holds the seat. States’ font color indicates which party is projected to win it (blue being Democrat and red being Republican).
Since Ohio is a full toss-up, it is not colored blue or red. West Virginia is the only state with an incumbent of one party that is seen as definitely going to flip. Of the 21 seats Democrats have to defend, only 11 of them are seen as definitely staying with that party. For Republicans, nine of the 11 seats are seen as definitely staying with that party.
There were a few seats that almost had a consensus that didn’t quite make it on this chart. Here are some examples:
- CNalysis rates Texas’ seat, currently held by Republican Ted Cruz, at Level 1, while the other four forecasters rate it as a Level 2.
- Inside Elections and CNalysis rate Florida’s seat, currently held by Republican Rick Scott, as Level 3, while the other three forecasters rate it as a Level 2. (Although CNalysis has it as “Very Likely R” instead of just “Likely R,” suggesting that it sees Florida as a borderline Level 3.)
- Split Ticket rates Montana’s seat, currently held by Democrat Jon Tester, at Level 1, while the other four forecasters rate it as a Level 0.
Key Races to Watch
Here are some of the key races to watch for that will decide whether the Democratic Party keeps the U.S. Senate majority or if the Republican Party takes it.
- Arizona: As noted previously, Kyrsten Sinema is not running for reelection. Sinema rankled many Democrats who accused her of being too moderate, and she even took the unusual step of leaving the party to become an independent. Arizona is going to be one of the battleground states deciding the presidential rematch between Biden and Trump as well, so that will inevitably have a major impact on the concurrent U.S. Senate race as well. Cook, Inside, and CNalysis rate this seat as a Level 0 (toss-up), which Sabato and Split Ticket see it as a Level 1 that slightly favors Democrats.
- Montana: Incumbent Democrat Jon Tester is seen as one of the likeliest of his party to lose his U.S. Senate seat. The forecasters in this article all sea the race as a toss-up (except for Split-Ticket, which sees the race as slightly favoring Republicans). But Tester isn’t a stranger to unfavorable odds. He won re-election in 2018 even though the state voted for Trump by more than 20 points and his first election to the seat in 2006 was within 1 point. Will he pull it off again for a fourth term in the chamber?
- Nevada: Nevada is seen as up for grabs in the presidential race and so is the U.S. Senate seat this year. Incumbent Democrat Jacky Rosen has a tall task ahead of her. Fellow Democrat Catherine Cortez Masto barely held onto her U.S. Senate seat in 2022, Republican Joe Lombardo won a close race for governor that year, and Trump is given a real chance of winning the state for his presidential campaign. The five forecasters in this article all see her race as a toss-up or only slightly favoring her. She defeated Republican incumbent Dean Heller by a 5-point margin in 2018 to get her current seat, but it’s quite possible that Republicans flip the script on her this year.
- Ohio: All five forecasters from above see the presidential race in Ohio as a Level 2 race favoring Trump, but the U.S. Senate race is a lot murkier. Sherrod Brown is considered another one of the likeliest Democrats to lose his seat, though the five forecasters all agree on it being a Level 0 race (toss-up). Being on the same ballot as Trump when he is expected to win Ohio may be enough to unseat Brown, but being an incumbent is generally an advantage, too.
- West Virginia: Long-time incumbent Democrat Joe Manchin is not running for re-election. Like with Sinema, some Democrats have criticized Manchin over the years as being too moderate. But West Virginia has become even more Republican in recent years, so it’s very unlikely Democrats will hold onto the state, even if Manchin were running again. West Virginia is the only state where the above five election forecasters all agree it’s likely to flip parties.
Possibilities for the U.S. Senate in November 2024
By sheer number of seats to defend for both parties, Republicans have a prime opportunity to take back the U.S. Senate majority. They only need a net gain of at least two seats. As of May 3, 2024, CNalysis sees an 83.2% chance for that to happen.
Republicans can still have the majority if they win one seat as long as Trump wins the presidential rematch against Biden — as Republicans would have the tie-breaking vote from whoever the vice president would be — but it would be a major missed opportunity. Republican U.S. Senators like Lisa Murkowski and Susan Collins have shown a willingness to buck Trump in the past, which would greatly limit the 50–50 advantage if Trump were to win again. The failure to capitalize on opportunity would be even more pronounced for Republicans if they only gained one seat and Biden won reelection.
Of the last five presidential elections, Trump’s victory in 2016 was the only time where the winning candidate’s party lost seats in the U.S. Senate. On the other hand, Republicans had a lot more seats to defend then than they do in 2024. Forecaster ratings can and will change over time, and there are still six months before the election. But the advantage is certainly on the Republicans’ side for the U.S. Senate this year.
