This was the announcement Senate Democrats had been dreading.
When it happened, it appeared to deal a major blow to their hopes of retaining their slim majority in the Senate in the 2024 elections.
“I have made one of the most difficult decisions of my life and have decided that I will not run for re-election to the United States Senate,” Democratic Senator Joe Manchin of West Virginia announced earlier this month.
Manchin, a moderate Democrat and former governor, won more than 60% of the vote in his 2012 re-election bid, but his margin of victory fell to just three points in 2018.
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The consensus was that Manchin is the only Democrat who can win in West Virginia next year after his state has shifted significantly to the right over the past decade. Former President Donald Trump won West Virginia by nearly 40 points in the 2020 election.
Democrats control the US Senate by a majority of 51 to 49, but Republicans are looking forward to a favorable Senate map in 2024, with Democrats defending 23 of the 34 seats. Three of those seats are in red states that Trump won in 2020 — West Virginia, Montana and Ohio.
Five other blue seats are in key swing states that President Biden narrowly won in 2020 — Arizona, Michigan, Nevada, Pennsylvania and Wisconsin.
With nine weeks to go until the first election, this candidate remains the front-runner in the Republican presidential race
“Democrats have multiple paths to protecting and strengthening our Senate majority, and they are in a strong position to achieve that goal,” David Bergstein, a spokesman for the Democratic Senatorial Campaign Committee, said in a statement after Manchin’s announcement.
“In addition to defending battle-tested incumbents, we have actually expanded the battleground map to include Texas and Florida,” Burstein added, referring to what he called “unpopular Republican incumbents.”
Texas and Florida, where incumbent Senators Ted Cruz and Rick Scott are seeking re-election, appear to be the only seats potentially competitive in next year’s GOP general election.
Here’s a look at the five seats most likely to flip in 2024.
With Manchin not seeking re-election, National Republican Senatorial Committee (NRSC) Chairman Sen. Steve Daines said: “We like our prospects in West Virginia.”
Right now, the main event is in the Republican Senate primary, where popular Democratic governor-turned-Republican Jim Justice has the backing of the NSC committee and Trump.
The Justice Party has raised more money than its main rival, Conservative MP Alex Mooney, who enjoys the support of the fiscally conservative Club for Growth.
The first Democrat to jump into the race after Manchin’s departure is 32-year-old Zachary Shrewsbury, a West Virginia native and Marine veteran.
Democrats breathed a sigh of relief when Sen. Jon Tester of Montana announced earlier this year that he would seek re-election in 2024 in a state that Trump carried by 16 points three years ago. The Democratic incumbent has taken in a whopping $15 million in fundraising so far this year.
Tim Sheehy, a former Navy SEAL and Purple Heart commander who has flown more than 200 missions in the wars in Iraq, Afghanistan and elsewhere around the world, launched a Republican Senate bid in late June.
Sheehy, CEO of Bridger Aerospace, a Montana-based firefighting and wildfire monitoring air services company, has support from the NRSC.
Rep. Matt Rosendahl, a hard-right congressman, is seriously considering making a bid. Rosendahl narrowly lost to Tester in the 2018 Senate election.
Longtime Democratic Sen. Sherrod Brown is the only member of his party to win a nonjudicial statewide election in Ohio in the past decade. With Brown running in 2024 for a fourth six-year term representing Ohio, he will be heavily targeted by Republicans in a state that was once a key general election battleground but has turned red over the past six years.
Trump carried Ohio by eight points in his 2016 presidential election victory and reelection defeat in 2020. Last year, Trump’s chosen Senate candidate in Ohio — Sen. J.D. Vance — edged out longtime Democratic Rep. Tim Ryan Best Points though, Ryan ran what political experts considered a nearly flawless campaign.
Brown, who served as a congressman, state legislator, and Ohio secretary of state during his nearly half-century career in electoral politics, is well known throughout the Buckeye State. The senator, known as a champion of populist causes, received $3.6 million in contributions during the first three months of this year.
Two Republicans who ran unsuccessfully for the 2022 GOP Senate nomination in Ohio are already vying to unseat Brown.
State Sen. Matt Dolan, a former district attorney and Ohio assistant attorney general, launched his campaign in January. Dolan, whose family owns Major League Baseball’s Cleveland Guardians, has spent millions of his own money running ads for his 2022 Senate bid.
He surged toward the end of the primary race, finishing third in a crowded field of Republican contenders, winning nearly a quarter of the votes.
In April, Bernie Moreno, a successful Cleveland-based businessman and luxury car giant, announced his candidacy. Moreno, an immigrant who arrived in the United States legally from Colombia with his family when he was a 5-year-old boy, also spent millions of his own money running television ads in an effort to boost his first bid for the Senate.
But he suspended his campaign in February 2022 after requesting a private meeting with Trump.
In July, Ohio Secretary of State Frank LaRose joined the race, launching a long-awaited Senate campaign.
With Democratic Sen.-turned-independent Kyrsten Sinema gearing up for her re-election campaign — though she has yet to officially announce one — the Senate race in battleground Arizona could be the most complicated of the 2024 cycle.
Democratic Rep. Ruben Gallego is already running on the left and has raised more money than Sinema, though the incumbent has a nice advantage in available cash.
Pinal County Mayor Mark Lamb recently became the first major GOP challenger to launch a campaign.
But Carrie Lake, the 2022 GOP gubernatorial nominee, instantly became the GOP front-runner when she jumped into the race in October. Lake, a former television news anchor and staunch Trump ally, narrowly lost the gubernatorial election last year but refused to concede.
The Keystone State, a perennial general election battleground, will likely live up to its reputation again in 2024, as it holds what is arguably one of the most competitive and expensive Senate races across the country.
Democratic Sen. Bob Casey, who served for a decade as state auditor general and then treasurer before winning his first Senate election in 2006, is seeking a fourth six-year term in office.
Casey, who is not expected to face any serious challenge in the Democratic primary, is the son of a popular former governor.
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Republicans appear mostly united behind Dave McCormick, who is making his second consecutive run for Senate.
McCormick, a former hedge fund executive, West Point graduate, Gulf War veteran and Treasury Department official under former President George W. Bush, received the Pennsylvania Republican Party’s endorsement in late September, shortly after entering the race.
McCormick has been courted by Republicans nationally and statewide to run, and his candidacy gives the GOP a high-profile candidate with the ability to bankroll his own race that is expected to be one of the most expensive in the country.
The Pennsylvania GOP’s endorsement would likely help McCormick avoid a crowded and combustible battle for the 2024 GOP Senate nomination like the one he faced last year. McCormick ended up narrowly losing the nomination to renowned physician and heart surgeon Mehmet Oz, who cruised to a primary win thanks to a late endorsement from Trump. Oz ended up losing the general election last November to Democrat John Fetterman.
Get the latest updates from the 2024 campaign trail, exclusive interviews and more in the Fox News Digital Election Center.