The main super PAC supporting Senate Republicans saw a “huge spike” in dark money contributions in 2025, a sign of the massive arsenal the GOP is building to protect its hold on Congress in November’s midterm elections, according to a new report from political reform group Issue One first reported by Raw Story.As Democrats aim to capitalize on the growing unpopularity of President Donald Trump and his Republican party and regain control of Congress, the Republican-aligned Senate Leadership Fund skyrocketed dark money contributions by 581 percent in 2025 compared to 2023.Michael Beckel, money in politics reform director at Issue One, said: “When you see an infusion of money like this, that usually means that these big money groups want to make sure that they have all of the resources they can muster to defend seats, to defend candidates, to defend their majority.”At the same time, Senate Democrats saw a drop in dark money donations, Issue One said.‘Arms race’Dark money is money donated to political groups without disclosure of the source, as enabled by Citizens United v. Federal Election Commission, a controversial Supreme Court decision from 2010.According to Issue One's analysis of campaign finance reports, in 2025 the Republican-aligned Senate Leadership Fund super PAC brought in $35 million from its affiliated dark money group, One Nation, representing $1 out of every $3 raised.In 2023, that number was $5.18 million, Beckel said. Four major super PACs increased 2025 dark money contributions by 65 percent, according to a new report. Graphic: Issue One)This indicates “just a surge of dark money coming into the main super PAC supporting Senate Republicans at a time when, clearly, there's a lot of political winds blowing that say Democrats have a fighting chance to win the U.S. House of Representatives and maybe even pick up seats in the Senate,” Beckel said.The four main super PACs focused on electing Democrats and Republicans in the House and Senate raised a combined $71 million from dark money sources in 2025: up 65 percent on the same point in the 2022 and 2024 election cycles, Issue One said.“Both sides see this as an arms race where they don't want to put down any weapon, and when you see just huge sums of money coming in to influence elections from unknown donors, that raises serious questions about who's trying to buy access and influence in Washington,” Beckel said.Republican and Democratic super PACs focused on the House maintained steady growth in dark money contributions, while the Senate Majority PAC, benefitting Democrats, received fewer dark money contributions in 2025, according to the report.For every $4 raised for the Republican-aligned Congressional Leadership Fund, nearly $1 came from dark money group American Action Network, which totaled $17 million in 2025, according to Issue One. On the Democratic side, about $1 of every $6 raised by the House Majority PAC and about $1 out of every $7 raised for Senate Majority PAC came from dark money group Majority Forward, totaling $11 million and $8 million in 2025.“We continue to see this escalating arms race, and it's deeply concerning when you've got so much money from unknown donors coming in on both sides of the aisle,” Beckel said.All four super PACs did not respond to Raw Story’s interview requests or declined to comment.‘Massive war chest’Beckel said he anticipates seeing significant amounts of dark money continuing to flow into these super PACs, especially around Senate races.“There's going to be a huge battle over control of not just the House but the Senate, and wealthy donors who are evading the spotlight are helping Senate Republicans raise a massive war chest through their super PAC to defend those seats,” Beckel said. Super PACs received massive dark money contributions ahead of 2024 election. Graphic: Issue One.Among Senate seats not up for re-election this year, Democrats hold 34 and Republicans 31. Two Democratic seats, held by Sen. Jon Ossoff in Georgia and in Michigan by retiring Sen. Gary Peters, and two Republican seats, held by Sen. Susan Collins in Maine and the North Carolina seat held by retiring Sen. Thom Tillis, are true toss-ups, according to the Cook Political Report.Democrats’ narrow path to regain the Senate majority would require picking up seats in Alaska, North Carolina, Ohio and Maine, according to Cook.During the 2023-24 election cycle, the four super PACs raised about $1 of every $5 from dark money groups. Dark money accounted for 21 percent of contributions to both parties’ Senate-focused PACs for the 2024 election, according to Issue One.Issue One supports the DISCLOSE Act, legislation focused on increasing transparency and curbing the influence of dark money, which House Democrats reintroduced on Wednesday.But with such a deeply divided Congress, Beckel said Issue One is focused on state-level reforms to reel in unlimited spending on elections by corporations and outside groups enabled by Citizens...