The 2024 Battle for the Senate Takes Shape

When Democratic Sen. Joe Manchin announced in November he would not seek re-election, he effectively took West Virginia off the 2024 map of Senate battleground states and greatly diminished Democrats’ odds of keeping their majority in the chamber. With popular Republican incumbent Gov. Jim Justice vying to fill Manchin’s seat, it’s nearly impossible to imagine any Democratic Senate candidate other than Manchin winning a state that, if the 2020 election is any guide, Joe Biden will likely lose by nearly 40 points in November. 

With arguably no good pickup opportunities elsewhere this cycle—and the current makeup of the Senate at 51-49—the best Democrats can reasonably hope for come January 2025 is a 50-50 Senate with Vice President Kamala Harris returning to the role of tiebreaker. 

Yet the stakes are higher than they might seem.

When Democrats last held a trifecta—controlling the House, Senate, and White House from 2021 to 2023—Manchin and Sen. Kyrsten Sinema of Arizona were there to prevent their fellow Democrats from spending an extra $4 trillion and keep them from effectively abolishing the legislative filibuster, the 60-vote hurdle that most legislation must overcome to make it through the upper chamber. Manchin and Sinema were the only two Democrats to vote against scrapping the 60-vote rule in January 2022, and Sinema’s stand resulted in her being purged from the party—she now is an independent who caucuses with Democrats and seems very unlikely to seek re-election.

If Democrats take back the House and Biden wins re-election, a 50-50 Senate without Manchin, Sinema, and the legislative filibuster—assuming Democrats push to abolish it again—would give Democrats much more power than they currently enjoy. Some items on the agenda could include sweeping legislation on federal elections and campaign finance; transgender rights and religious liberty; the abolition of the Hyde Amendment that prohibits taxpayer funding of elective abortions; a federal abortion law that goes beyond Roe; and legislation to add the District of Columbia and Puerto Rico as states, potentially handing Democrats four extra Senate seats. Packing the Supreme Court would require many congressional Democrats—and Biden himself—to change their stated positions, but the threat would certainly be more potent with a filibuster-free Senate. 

But the prospect of Democrats holding onto their majority is very much in doubt, as Democratic incumbents will have to fend off challenges in two red states—Montana and Ohio—where Biden will likely lose by a wide margin in November. Democratic-held seats in Wisconsin, Pennsylvania, Michigan, Arizona, and Nevada—all presidential battlegrounds—are also up for grabs. And earlier this month, Larry Hogan, a popular former governor, put the Maryland Senate race in play for Republicans. As for Democratic pickup opportunities, their best shots are in red Florida and redder Texas.

While a lot can change between now and Election Day, here’s a look at the top Senate races to watch in 2024.

Montana and Ohio

Montana is the state most likely to flip from blue to red and give Republicans a 51st vote in the Senate, and that’s why a whopping $120 million in TV advertising has already been reserved or spent in the race, according to Ad Impact. 

Biden lost the state by 16 points in 2020, so the big question is just how far Sen. Jon Tester, a three-term Democratic incumbent, can run ahead of the top of the ticket. Tester has defied the odds before: In 2012, he won his re-election campaign by 4 points while Mitt Romney defeated Barack Obama by 14 points in Montana. But more than a decade later, there’s a lot less ticket-splitting in the state. In 2012, Democrat Steve Bullock narrowly won his first race for governor with 49 percent of the vote, while Barack Obama lost the state to Mitt Romney with 42 percent of the vote. When Bullock ran for Senate in 2020, however, he lost to Republican Sen. Steve Daines by 10 points, securing only 45 percent of the vote to Biden’s 41 percent. A similar overperformance in 2024 won’t be enough to save Tester. 

Tester got bad news last week when GOP Rep. Matt Rosendale announced he would bow out of the Senate race just days after joining it, thus sparing the Trump-endorsed former Navy SEAL and businessman Tim Sheehy a bruising primary. “It’s a really big deal,” said Jessica Taylor, who closely follows Senate races for the Cook Political Report. “The race contours would have looked very different if it was Rosendale vs. Tester instead of Sheehy vs. Tester.”

Rosendale had already run against Tester—he lost to him by 3.5 points in 2018—and he was widely thought to be a weaker candidate than Sheehy. That’s why the National Republican Senatorial Committee endorsed Sheehy early in the race and why Senate Democrats’ main super PAC spent nearly $6 million trying to tear Sheehy down and boost Rosendale. 

A February poll by SurveyUSA showed Tester leading Sheehy 49 percent to 40 percent, but internal GOP polling shows a much closer race with Tester’s level of support in the low 40s. 

Ohio is probably the next best pickup opportunity for Republicans, as Trump carried the state by 8 points in both the 2016 and 2020 presidential elections. Incumbent Democratic Sen. Sherrod Brown, therefore, has a steep hill to climb—but only about half as steep as the one facing Tester in Montana.

Brown won re-election by about 7 points in the blue wave of 2018 at the same time as Republican Mike DeWine won the gubernatorial race by 4 points. A similar overperformance in 2024 would likely keep Brown in the Senate.

With less than a month to go before the Ohio GOP Senate primary, businessman Bernie Moreno is the odds-on favorite to win the nomination over Ohio Secretary of State Frank LaRose and state Sen. Matt Dolan. Moreno has the backing of both Trump and the Club for Growth. Polling from the summer and fall of 2023 showed Moreno faring worse than LaRose or Dolan against Brown, but an Emerson poll conducted in January showed Brown barely leading Moreno 39 percent to 37 percent.

Presidential Battlegrounds and Maryland

Although Montana and Ohio will likely determine whether Republicans or Democrats control the Senate, Republicans have an opportunity to make gains in six more states, four of which Trump narrowly won in 2016 before narrowly losing in 2020: Arizona, Michigan, Pennsylvania, and Wisconsin.

In Arizona, Sinema’s lack of both fundraising and effort to gather the necessary signatures to run for re-election indicates she’s heading for retirement. That would set up a race between MAGA darling Kari Lake and progressive darling Rep. Ruben Gallego, a 44-year-old Marine Corps veteran who has served in Congress since 2015. Lake, a former TV news anchor, lost the 2022 gubernatorial race in the state by less than a point after going all-in on Trump’s “stop the steal” conspiracies and telling John McCain voters to “get the hell out” of a campaign event. She tried this week to walk those comments back and call for GOP unity, but was loudly rebuffed by McCain’s daughter Meghan. With progressive Gallego instead of maverick Sinema as the Democratic nominee, it’s hard to see either Senate candidate overperforming or underperforming the top of the ticket by much. Trump lost Arizona to Biden by 0.3 points in 2020, four years after he won the state by 3.5 points.

In Michigan, Democratic Rep. Elissa Slotkin has all but wrapped up the primary but is facing a tough general election race as she seeks to replace retiring Sen. Debbie Stabenow, a fellow Democrat. Trump lost the state to Biden by 3 points in 2020, but the latest Detroit Free Press poll conducted by EPIC-MRA showed Biden trailing Trump there by 4 points—41 percent to 45 percent. The same survey found Slotkin, a former CIA analyst and Pentagon official, leading former Republican Rep. Mike Rogers 39 percent to 38 percent. The August GOP primary is shaping up to be a competitive race between Rogers and businessman Sandy Pensler. Former GOP congressman Peter Meijer is also seeking the nomination after losing his House seat in 2022 in a primary race.

In Wisconsin, Democratic incumbent Sen. Tammy Baldwin will likely face off against Republican Eric Hovde, an investor who announced his campaign on Tuesday. In a state that Trump lost by less than a point in 2020 and won by less than a point in 2016, Baldwin likely wouldn’t need to run that far ahead of Biden (if at all) in 2024 to secure a third term. She has proven to be a strong candidate in the past—she won re-election by 11 points in 2018—but a recent Marquette University Law School poll showed her net favorability rating at -3 percent in the state. Though it remains to be seen if Hovde, who lost a 2012 primary race against former governor Tommy Thompson, will draw a serious primary challenger, national Republicans hope his ability to spend $20 million of his own money on the race will clear the field. 

In Pennsylvania, Democratic incumbent Sen. Bob Casey Jr. will face off against Dave McCormick, the hedge-fund investor, George W. Bush administration alum, and Army veteran who narrowly lost his bid for the 2022 GOP Senate nomination to the Trump-backed celebrity doctor Mehmet Oz. Casey, the son of the state’s former governor, has a strong political pedigree and won his last campaign for re-election in 2018 by 13 points. Pennsylvania is another state Trump won by about a point in 2016 and lost by a point in 2020. McCormick’s campaign and super PAC are sure to be well-funded, but his electoral hopes are closely tied to the top of the ticket. Polling in the presidential race has been all over the map: Emerson recently showed Trump leading by 5 points, while Franklin & Marshall found Biden leading by 5 points.

In Nevada, Democratic incumbent Sen. Jacky Rosen will likely face off against Sam Brown, a retired Army captain and Purple Heart recipient who was wounded and disfigured while serving in Afghanistan. While Brown faces a primary, Taylor—the Cook Political Report analyst—said he’s the “clear favorite.” Polls have shown surprising strength for Republicans in Nevada: Trump currently leads Biden by 7 points in the RealClearPolitics polling average. Democrats in Nevada have outperformed their poll numbers many times in the past, but not often by that wide of a margin. It’s difficult to see Rosen, who has done little to distinguish herself during her first term, running far ahead of Biden in November.

In Maryland, Larry Hogan turned heads when he unexpectedly announced a Senate campaign earlier this month for the seat being vacated by retiring Sen. Ben Cardin. The popular former governor—and son of a three-term congressman from the state—scored his first upset in deep blue Maryland in 2014 and won re-election by 12 points in 2018, but he’s signed up for a very daunting task in 2024. Given how the 2020 election played out in the state, he will likely need to run more than 30 points ahead of Trump to have a chance of winning—which might explain why he launched his campaign by saying he will “stand up to both parties.” Democratic Rep. David Trone and Prince George’s County Executive Angela Alsobrooks are facing off in the Democratic primary, and a February Emerson poll showed Hogan tied with Trone—42 percent apiece—but leading Alsobrooks 44 percent to 37 percent. Before he decided to jump in the race, Hogan’s longtime pollster Ragnar Research Partners found Hogan leading both Trone and Alsobrooks by double digits.

Florida and Texas

The only Republican Senate seats that might end up in play this year are those held by Sen. Rick Scott of Florida and Sen. Ted Cruz of Texas.

In Florida, Scott seems likely to face former Democratic Rep. Debbie Mucarsel-Powell, who was encouraged to run by Chuck Schumer. Trump only won Florida by 3.3 points in 2020, but the state has trended redder in the years since, with Gov. Ron DeSantis winning re-election in 2022 by nearly 20 points. There hasn’t been any independent public polling of the race, but it would take a significant lurch to the left for Democrats to oust Scott in 2024.

In Texas, Cruz narrowly won re-election in the 2018 blue wave, beating then-Rep. Beto O’Rourke by 2.6 points, but Trump defeated Biden in the state by a healthier 5.6 points in 2020, when Republican Sen. John Cornyn won re-election by nearly 10 points. Cruz has drawn a Democratic challenger with an appealing biography—former Tennessee Titan and current U.S. Rep. Colin Allred—but it’s difficult to see Trump losing Texas or Cruz running far behind his party’s standard bearer. A February YouGov poll found both Democrats seeking the nomination—Allred and Texas state Sen. Roland Gutierrez—trailing Cruz by 14 points.

Any of these races could become more or less competitive as November approaches, but with eight months to go, anything from a narrow—but much more powerful—Democratic Senate majority to a sizable Republican majority is possible.