Democrats will be on the defensive in 2024 as they try to preserve or expand their slim, one-seat lead in the Senate, but recent campaign finance filings show their candidates in key states have built up substantial war chests — and, in some cases, outraised potential Republican opponents heading into the summer.

Competitive races this cycle are almost entirely expected to be contests for seats held by Democrats or Democrat-aligned independents. The GOP holds just 11 of the 34 seats that are up for election next fall, with Democrats defending 20. Another three are held by independents who caucus with the Democrats.

Senate Democrats in Montana, Ohio, Pennsylvania, West Virginia and Wisconsin are all expected to face well-funded Republican challengers in states that either supported former President Donald Trump or went into President Joe Biden’s column by around 1%. In Arizona, independent Kyrsten Sinema left the Democratic Party but has not said if she plans to run for reelection in a state where Biden won by just over 10,000 votes. 

Arizona

While her future remains unclear, Sinema brought in just under $1.7 million to boost her coffers to $10.8 million. If she were to run again, she could face both challengers from both sides, with a Democratic congressman and a Trump-aligned sheriff already raising money to take her on.

Since entering the race in January, Arizona Rep. Ruben Gallego raised nearly $7 million, including $3.1 million in the second quarter, nearly doubling what Sinema has raised all year. Already spending heavily, to the tune of $4.3 million in five months, Gallego will need to keep up the fundraising pace. The five-term congressman who entered the race with explicit designs to oust Sinema, whose centrist streak has frustrated her Democratic allies in Congress and the White House, has around $2.7 million in the bank, over three times less than the incumbent senator.

So far, only one major Republican candidate has entered the race in the battleground state: Pinal County Sheriff Mark Lamb. Lamb earned celebrity status on the American right through his allegiance to Trump and his hawkish prescriptions for illegal immigration — “it’s time to declare the drug cartels terrorist organizations and use military force to wipe them out, just like we did to ISIS,” he said in the first ad of his campaign.

But he’s brought in only $607,000 since announcing in April and had just $335,000 cash on hand at the end of the quarter.

Former TV news anchor-turned-gubernatorial candidate Kari Lake has said she is considering running in the Republican primary and will decide in the coming months. Her star on the right is even brighter than Lamb’s, having grown as she embraced and promoted conspiracies about the COVID-19 pandemic and the 2020 presidential election. She has unsuccessfully pursued legal challenges to the results of her 2022 race for governor based on similar conspiracies after she lost to Democrat Katie Hobbs by 17,000 votes.

Montana

In deep-red Montana, Democratic Sen. Jon Tester will try to stave off extinction in pursuit of a fourth term, but will need substantial capital to do so. His fellow senator from Montana, Republican Steve Daines, has been tasked by Senate Minority Leader Mitch McConnell with ending his career as head of the Senate GOP's campaign arm, the National Republican Senatorial Committee.

In three months, Tester brought in over $5 million, leaving his campaign with $10.5 million to take into the summer and the fall. The only Republican in the race expected to have significant financial backing launched their campaign last month, so they have yet to report any contributions to the FEC.

But Tim Sheehy, a former Navy SEAL and the CEO of an aerial firefighting company, will have the backing of Daines and the NRSC, which raised $30 million in the first six months of this year to help Republicans retake the Senate.

“Tim Sheehy is a decorated veteran, successful businessman and a great Montanan,” Daines said in a statement when Sheehy announced. “I could not be happier that he has decided to enter the Montana Senate race.”

Right-wing Rep. Mat Rosendale, who lost to Tester in 2018, has said he is considering a run and has been publicly encouraged by Sens. Ted Cruz, R-Texas, and Mike Lee, R-Utah. In the 2018 election, he brought in $6 million to Tester’s $21.3 million.

“If we can avoid a contentious primary, that’d be the best thing,” Daines told CBS News last week.

Ohio

Ohio was long viewed as a battleground where both parties could contend, but Trump won the state twice and Republicans have held onto the governorship for over a decade and one Senate seat for over 20 years. The only Democrat to have success statewide since Obama won Ohio twice is progressive Sen. Sherrod Brown, who first took office in 2007. In 2018, Brown secured his third Senate term with a nearly 7 percentage point victory over a Republican congressman.

In what may be his toughest electoral environment yet, Brown is raising money early, bringing in $5 million in the second quarter to keep his accounts flush. As of June 30, he has $8.7 million to work with.

Three prominent Republicans have begun battling for the chance to take on Brown, with Ohio Secretary of State Frank LaRose launching his campaign on Monday.

“I’m a Green Beret, a conservative, a man of faith, and I’m not afraid of a fight,” LaRose said in his announcement video.

LaRose will have to contend with opponents who have millions in their coffers and racked up endorsements. State Sen. Matt Dolan, whose family owns the Cleveland Guardians, raised $308,000 and loaned his campaign $1 million in the second quarter, after already loaning himself $3 million previously. He spent nearly $8 million on an unsuccessful Senate bid in 2022, coming in third with 23% of the vote in the Republican primary.

Ohio’s junior senator, J.D. Vance, beat Dolan in that primary and is now endorsing his rival, car dealership owner Bernie Moreno, a favored candidate of the party’s right-wing and Trump. The former president called Moreno a “highly respected businessman” who “would not be easy to beat.” Moreno raised $2.3 million since announcing his run in April and has $1.5 million in the bank.

Pennsylvania

After a disastrous 2022 election that saw them lose in both the Senate and governor races, Pennsylvania Republicans have yet to produce a candidate to take on Sen. Bob Casey in 2024. But Casey isn’t taking any chances.

Casey, who has served in statewide office since 1997, brought in $4 million in the last three months, his best fundraising quarter ever according to his campaign. His campaign also touted that 75% of his contributions were under $50. High quantities of low dollar donors are viewed by campaigns as an important resource that candidates can return to for cash over the course of a race.

“This impressive fundraising quarter shows Bob Casey is one of the most formidable incumbent Senators in the country, with the statewide support to prove it,” Casey’s campaign manager Tiernan Donohue said in a statement.

State Sen. Doug Mastriano, a far-right Christian nationalist, said in May he wouldn’t run for Senate after losing the gubernatorial race in 2022. Former hedge fund executive David McCormick lost to Mehmet Oz, the celebrity doctor, by 1,000 votes in the 2022 GOP Senate primary and is reportedly considering another run. 

"I want to see candidates that can win not only a primary election, but importantly can win a general election and appeal to independent voters," Daines, the Montana Republican leading his party’s Senate electoral efforts, told Reuters last week. "David McCormick would fit that profile."

West Virginia

In the reddest battleground state on the Senate map, West Virginia, Democratic Sen. Joe Manchin raised just under $1.3 million between April 1 and June 30, his most recent filings with the Federal Election Commission shows. Though he has not yet ruled out a third-party run for president, nor has he formally launched a reelection bid, Manchin has $10 million in the bank so far to take on a Republican challenger in his home state if he decides another go at the Senate.

The two Republicans vying for a chance to beat him, Gov. Jim Justice and Rep. Alex Mooney, both have less than $1 million in their accounts. If he runs, Manchin will need all the dollars he can get in a state that voted for Trump by nearly 40% in 2020.

Wisconsin

While she does not yet have a Republican opponent, Sen. Tammy Baldwin has raised nearly $5.5 million this year, including $3.3 million last quarter, as she prepares for an election the GOP considers a top priority in 2024. Her campaign says that number is the most raised by a Wisconsin Senate race in a single quarter the year prior to the election.

Wisconsin Rep. Mike Gallagher turned down Republican leaderships’ efforts to get him to run, saying in June he would stay in the House to focus on his efforts to “confront the Chinese Communist Party threat.”

Rep. Tom Tiffany told Spectrum News in June he would decide on a run by August.

Other Republican targets include Nevada and Michigan, the latter of which has crowded fields running both primaries to replace the retiring Sen. Debbie Stabenow, a Democrat. The NRSC said it plans to “aggressively target” the Michigan seat, but has yet to get behind any one candidate. Rep. Elissa Slotkin, a Democrat, is the only candidate in either party to raise significant funds so far, bringing in just under $3 million in the last quarter and ending with $3.7 million in the bank.

In Nevada, the NRSC has expressed support for Sam Brown, a retired U.S. Army captain who sustained significant scarring from an explosion while serving in Afghanistan. Brown announced last week his bid to unseat incumbent Democratic Sen. Jacky Rosen, who brought in $2.7 million in the last three months and reported having nearly $7.5 million heading into the summer and fall.