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Senate Democrats are gearing up for what’s expected to be a challenging reelection environment in 2024 even as they await the results of a Senate runoff in Georgia between Sen. Raphael Warnock (D) and Republican Herschel Walker next month.

About two dozen Democrats or those who caucus with the party will be up for reelection, and several are expected to face stiff competition — some from within their own party. 

Here are the eight most vulnerable Senate Democrats up for reelection in 2024:

Sen. Joe Manchin (D-W.Va.)

Senate Energy and Natural Resources Committee Chairman Joe Manchin (D-W.Va.)

Manchin hails from a state former President Trump won by close to 40 points in 2020 and is known for rattling Democrats and Republicans alike.

He upset Democrats by refusing to support eliminating the filibuster and by announcing late last year he couldn’t support President Biden’s climate and social spending reconciliation package.

But he later angered the GOP when he announced a deal with Senate Majority Leader Charles Schumer (D-N.Y.) to pass a separate climate, health care and tax package. 

Manchin won his first full term in 2012 by a comfortable margin and prevailed by 3 points in 2018. But he will almost certainly be among Republicans’ top targets in 2024.

At least one candidate has already jumped into the race to oust Manchin: Rep. Alex Mooney (R-W.Va.) announced earlier this month he would be making a bid against the senator. And West Virginia Gov. Jim Justice (R) said Tuesday he’s “very seriously” considering a Senate run.

Sen. Kyrsten Sinema (D-Ariz.)

Sen. Kyrsten Sinema, D-Ariz., arrives for a meeting of the Senate Homeland Security Committee at the Capitol in Washington, Wednesday, Aug. 3, 2022.

Like Manchin, Sinema has angered many within her party and could face a serious primary challenge. Republicans will also likely view the state as a top pickup opportunity.

Sinema has defended keeping the filibuster in place and has leveraged her party’s slim 50-50 Senate majority to notch concessions, including a deal she negotiated with Schumer earlier this summer that eliminated a carried interest loophole from Democrats’ climate and health care spending package.

That’s left some senators like Sen. Bernie Sanders (I-Vt.) expressing an openness to endorsing primary challengers to Sinema and Manchin. Rep. Ruben Gallego (D-Ariz.) has said he’s been approached about challenging the Arizona centrist and has been openly critical of Sinema, but has not committed to mounting a bid. 

Republicans, smarting from losses in the state in 2020 and 2022, are also eyeing the seat closely.

Sen. Sherrod Brown (D-Ohio)

Senate Banking, Housing, and Urban Affairs Committee Chairman Sherrod Brown (D-Ohio)

Brown cruised to victory by winning more than 50 percent of the vote against GOP candidates in three consecutive elections, but he’s the only statewide elected Democrat in a state that’s increasingly trending red.

While Ohio was long seen as a swing state, it voted for Trump twice after twice electing former President Obama, and this year Rep. Tim Ryan (D), who ran for retiring Sen. Rob Portman’s (R) seat, lost his race against Republican Sen.-elect J.D. Vance. 

That’s left some Democrats nervous and Republicans hopeful about 2024, though Brown’s record of statewide wins in Ohio could mean he has a clearer path to victory than Ryan had.

Sen. Jon Tester (D-Mont.)

Tester has run successfully for Senate three times and outperformed Obama in Montana in 2012, but his seat will likely be viewed as a key GOP pickup opportunity in 2024.

The Treasure State hasn’t shied away from electing Democrats. The party held the governorship between 2005 and 2021 and has sent 14 Democrats to the Senate, including Tester, since 1900 compared to just five Republicans. But it’s also a state that has gone overwhelmingly for the GOP presidential candidate — it voted for Mitt Romney in 2012 by more than 13 points and for Trump by 20 points and 16 points in 2016 and 2020 respectively.

Tester has been outspoken about his party’s lack of outreach to rural voters, saying in a podcast appearance earlier this year, “I honestly don’t think the Democratic Party can be a majority party unless we start appealing to middle America a lot more” — a theme that Democrats may have to grapple with in Montana and elsewhere.

Sen. Jacky Rosen (D-Nev.)

Nevada was home to one of the closest Senate battles in 2022, and while Sen. Catherine Cortez Masto (D) ultimately prevailed over her GOP challenger, Republicans could again see the state as a prime pickup opportunity two years later.

A former synagogue president and computer programmer, Rosen won her first term in the Senate by 5 points against Sen. Dean Heller (R) in 2018, the only election that cycle where a Democrat ousted an incumbent Senate Republican.

Nevada has emerged as a purple state. Cortez Masto won her race this year, but Gov. Steve Sisolak (D) was narrowly ousted by Republican Joe Lombardo. At the same time, the state’s voters have gone for Democratic presidential nominees in the last four cycles, which could help Rosen in a presidential election year.

Sen. Bob Casey (D-Pa.)

After losing outgoing Sen. Pat Toomey’s (R-Pa.) seat to Sen.-elect John Fetterman (D), Republicans will be eyeing a 2024 comeback with Casey up for reelection. 

A three-term incumbent and the son of former Pennsylvania Gov. Robert P. Casey Sr. (D), the low-key senator has at times changed his political thinking on key issues like gun control and abortion. 

In the wake of high-profile shootings in Buffalo, N.Y., and Uvalde, Texas, Casey earlier this year pushed Congress for more gun control measures like expanding background checks while acknowledging that his stance had evolved since he first served in the Senate. And while the senator is anti-abortion, in May he announced supporting legislation to codify abortion rights in light of a leaked Supreme Court draft ruling that indicated the high court would overturn Roe v. Wade. 

Sen. Tammy Baldwin (D-Wis.)

Sen. Tammy Baldwin (D-Wis.)

Baldwin is up for a third term in Wisconsin, a state that has delivered nail-biters to Democrats and Republicans alike. Trump won the state by less than a point in 2016, and Biden did the same in 2020. 

Republican Sen. Ron Johnson won his own third term in 2022 by 1 percentage point.

Baldwin made history when she became the first woman from Wisconsin to serve in the Senate in addition to being the first openly gay candidate to be elected to the upper chamber. Among the issues that Baldwin has advocated for have included expanding Medicaid to states that opted not to fully expand the program and codifying same-sex marriage protections.

Sen. Debbie Stabenow (D-Mich.)

Sen. Debbie Stabenow (D-Mich.)

Stabenow, who was first elected to represent Michigan in the Senate in 2000, will be up for reelection for a fifth term. Though she hails from a swing state that went for Trump in 2016 by less a percentage point and then for Biden in 2020 by close to 3 points, Stabenow has generally prevailed by much wider margins. 

Save for her first election in 2000, when she won against Republican Spencer Abraham by a percentage point, she’s since won reelection by wider margins, including double digits in 2006 and 2012. 

Still, Sen. Gary Peters’s (D-Mich.) election in 2020, when he eked out a win against Republican John James by just over a point, suggests the state is likely to be a top target for Republicans going into 2024. 

–Updated at 7:29 a.m.