Not all of that spending is traceable to a donor. "Dark money" refers to spending by groups — typically 501(c)(4) "social welfare" nonprofits and trade associations — that are not required to disclose who funds them.
OpenSecrets tracked $139 million in such spending in 2010 and roughly $180–313 million in the cycles that followed — counting only what non-disclosing groups reported to the FEC. Using a broader method that also captures undisclosed television and digital advertising, OpenSecrets put 2020 dark money at about $1 billion, and the Brennan Center — building on that method — estimated a record $1.9 billion in 2024. By the Brennan Center's accounting, dark money groups have spent at least $4.3 billion on federal elections since Citizens United.
The 2024 money also moved differently. Direct spending reported to the FEC — the only slice the public sees in real time — was just $43 million, under 2.5% of the total. The rest flowed through harder-to-trace channels: about $1.3 billion in contributions to allied super PACs, $315 million in online ads, and $242 million in television. Roughly $1.2 billion of the 2024 total backed Democrats and about $664 million backed Republicans — a partisan tilt that, before 2018, ran the other way.
A note on the numbers: the 2010–2016 figures and the 2020–2024 figures come from two different methodologies and are not directly comparable. The early figures count only spending reported to the FEC by non-disclosing groups; the later figures add undisclosed TV and digital advertising. The jump partly reflects better measurement — but every serious estimate points the same direction: up, and steeply.