These are the top Senate races to watch in 2024

Democrats grew their Senate majority in 2022. They'll be lucky to keep those gains in 2024.

Republicans, who took over the House following November's midterm elections, are hoping to replicate that success in the Senate next year. They have reason to be hopeful: Democrats face a daunting 2024 Senate map that puts them on defense in 23 of the cycle's 34 races, including multiple seats considered ripe for GOP challenges.

In some of the most vulnerable contests, Democrats are trying to hold on to Senate seats in states that voted for former President Donald Trump over President Joe Biden in the 2020 presidential election.

The grim outlook has some Senate Democrats considering retirement, even after the caucus expanded to a 51-49 majority following a better-than-expected showing in the midterms.

Here are some of the top Senate races to watch:

Sen. Joe Manchin may be one of the most conservative Democrats in the Senate, but his party affiliation still imperils his chances for reelection in deep-red West Virginia, which favored Trump by nearly 40 percentage points in 2020.

That may be why Manchin still hasn't announced whether he intends to run again — or why he has resisted even acknowledging he is a Democrat in public.

Manchin's potential Republican challengers aren't waiting for the incumbent to reveal his plans. Rep. Alex Mooney, whom Trump backed for his successful House race in 2022, has already netted a $10 million pledge of support from the conservative Club for Growth for his Senate primary run.

Manchin's campaign had $9.7 million in cash on hand as of the end of March, FEC filings showed.

But Manchin's biggest possible GOP rival could be West Virginia Gov. Jim Justice, reportedly the state's richest man and one of its favored contenders for the Senate race.

Election analysts at Sabato's Crystal Ball in January gave West Virginia a "Leans R" rating, making it the most vulnerable Democrat-held Senate seat of the cycle.

Manchin, who won his 2018 Senate race by about three percentage points, has recently put some distance between himself and his fellow Democrats. He even vowed to vote to repeal the Inflation Reduction Act, Biden's signature spending bill that Manchin helped pass, while complaining on Fox News that the administration had broken its word.

Democrats and Republicans alike are taking aim at the Arizona seat held by Sen. Kyrsten Sinema, who in late 2022 left the Democratic Party to become an independent.

The switch from Sinema, who continues to caucus with the Democrats, allows her to skip a potentially bruising Senate primary fight and compete directly in the general election.

But the move does not guarantee her a path to victory in the state, which is considered a toss-up and a prime takeover opportunity. Sinema has yet to announce if she will seek reelection in 2024.

Once considered a progressive Democrat, Sinema has taken a moderate tack in recent years. She drew criticism from some in her former party over her vote against a minimum-wage hike and her opposition to changing the filibuster.

She now faces a potential challenge from her left in Democratic Rep. Ruben Gallego, who has reportedly outraised Sinema as he vies for her job.

Republican Sheriff Mark Lamb has also jumped into the race. He could face off in a GOP primary against Kari Lake, the former TV news anchor who lost to Democrat Katie Hobbs in Arizona's 2022 gubernatorial race and is now considering a Senate bid.

If Sinema runs, the Arizona Senate race could become a three-way matchup. It's far from clear who would have the advantage in the swing state, which Biden won over Trump in 2020 by less than one percentage point.

While Sinema's independent label could draw appeal in a state where registration in the two major parties is rivaled by "Other," polls show the senator remains unpopular.

Sen. Jon Tester is one of three Democrats in the 2024 cycle who is defending a seat in a state that voted for Trump in the last presidential election. The Republican ex-president won Montana by about 16 points in 2020.

Tester's seat is considered a toss-up by Sabato's Crystal Ball, though the Cook Political Report says the seat leans in Democrats' favor.

Tester's decision to run again is welcome news for Democrats, who otherwise would have lost the incumbent advantage in a solid-red state.

But he could still face a formidable threat from his eventual Republican challenger. Former Interior Secretary Ryan Zinke, Rep. Matt Rosendale and Gov. Greg Gianforte have been eyed as possible contenders.

Democratic Sen. Sherrod Brown has held his seat since 2007, and he has already announced his plans for a fourth term in office.

But the 2024 Senate race in Ohio is currently considered a toss-up, as Republicans have made significant gains in the state in the last two election cycles.

Trump won the Buckeye State by more than eight points in 2020, and GOP candidates he endorsed, including now-Sen. J.D. Vance and Gov. Mike DeWine, won in the midterms.

Matt Dolan, a state senator and partial owner of the Cleveland Guardians baseball team who competed in the 2022 Republican Senate primary, is running for Brown's seat in 2024. Bernie Moreno, another Republican contender for the Senate seat, drew scrutiny when he suggested that there should be reparations for the descendants of Union Civil War soldiers "who died to save the lives of Black people."

Democrats in 2024 will be defending an open Senate seat in Michigan, a swing state that voted for Trump in 2016 and Biden in 2020.

Sen. Debbie Stabenow's surprise decision not to seek a fifth term erased Democrats' incumbent advantage over the seat, with no clear successor lined up to run at the time.

Democrats won major gains in Michigan in the 2022 midterms, taking control of the state House and Senate and securing another term for Gov. Gretchen Whitmer.

Republicans Michael Hoover and Nikki Snyder have so far entered the race for Stabenow's Senate seat.

On the Democratic side, Rep. Elissa Slotkin, who won a tough House reelection fight in the midterms, is seen as the top contender for the seat. Slotkin was endorsed in 2022 by former Rep. Liz Cheney, a Republican whose vocal criticism of Trump following the Jan. 6 Capitol riot triggered a break with her party's leadership and much of its rank and file in the House.

Sabato's Crystal Ball and the Cook Political Report both say the Michigan Senate race leans Democratic.

Unlike most of the other races on this list, in the California race there's little question that Democrats will hold on to the Senate seat that is set to open up in 2024.

Democratic Sen. Dianne Feinstein, who held the seat for three decades, at age 89 announced she would retire at the end of her current term.

By that time, multiple Democrats had already launched their campaigns for her job. The list of declared candidates so far includes Reps. Adam Schiff, Katie Porter and Barbara Lee, with more potentially on the way.

Feinstein, the oldest member of the U.S. Senate, took a monthslong leave in the spring due to health problems. Concerns about Feinstein's fitness for office quickly became a point of conflict among Democrats, with some openly calling for the senior senator's immediate resignation and others defending her. Feinstein's absence from the Senate Judiciary Committee has slowed Democrats' efforts to advance Biden's judicial nominees.

Trump narrowly lost Nevada to Biden in 2020, and his handpicked Republican candidate Adam Laxalt lost an even closer race for Democratic Sen. Catherine Cortez Masto's seat in 2022.

Now the state's other Democratic senator, Jacky Rosen, is seeking reelection in 2024. Her slate of potential Republican challengers appears slim so far.

Laxalt's name has come up as a potential 2024 Senate candidate, but the former Nevada attorney general in April signed on to help lead a super PAC encouraging Florida Gov. Ron DeSantis to run for president in 2024.