What is a 501(c)(4)
The answer
A 501(c)(4) is a tax-exempt "social welfare" nonprofit. It can run political ads, fund a Super PAC, or attack a candidate by name, and it never has to say who paid for it. The loophole is a legal one, the tax code allows political activity as long as it isn't the group's primary purpose, and the IRS has never clearly defined where that line sits or reliably enforced it. The folk model expects a nonprofit's political spending to be capped and named. The plain mechanic is that "primary purpose" was never given a bright-line number, so groups structure spending to sit inside an ambiguity nobody polices.
How it actually works
The rule comes from the IRS code section covering social welfare organizations. Unlike a 501(c)(3) charity, which cannot engage in campaign politics at all, a 501(c)(4) can, as long as politics stays secondary to its stated social welfare mission. The commonly cited rule of thumb is that political spending should stay under half of total spending, but this isn't a bright-line statute.1 The IRS applies a vague, case-by-case standard, and groups routinely structure their spending to stay just inside whatever ambiguity that standard allows.
Crucially, a 501(c)(4) never has to disclose its donors, even while running expressly political ads or wiring money to a Super PAC.1 That single feature is what makes it the standard dark money vehicle. Compare it to a PAC, which must name every donor above $200.
The IRS's willingness to police this line collapsed after 2013, when it emerged that the agency had flagged nonprofit applications using terms like "Tea Party" and "patriot" for extra scrutiny. A 2017 Treasury Inspector General report found the IRS had actually used both conservative and liberal keywords for screening between 2004 and 2013, complicating the initial one-sided political-targeting narrative.2 But the backlash was severe enough that, per ProPublica's reporting, it left the IRS's exempt-organizations division reluctant to closely examine 501(c)(4) political activity in the years since, softening enforcement of the primary purpose test regardless of who benefits from that softness.3
Donor-advised funds add a second layer of anonymity on top. A donor gives to a DAF sponsored by a firm like Fidelity Charitable, takes an immediate tax deduction, and the DAF, not the individual, appears as the grantor on the recipient's tax filings. DeSmog's October 2024 investigation of IRS Form 990 filings found that Fidelity Charitable, Schwab Charitable, and Vanguard Charitable together funneled at least $171 million since 2020 to nonprofits affiliated with Project 2025, with Fidelity Charitable alone responsible for more than $82 million of that across 68 groups.4 That figure comes from a single investigative outlet and hasn't been independently cross-verified, and it's specific to Project 2025-linked recipients, not dark money overall.
Who holds the power
Whoever runs the 501(c)(4) chooses the messaging and the money's next destination. The people who funded it, sometimes further hidden behind a donor-advised fund, take a tax deduction and full anonymity.
Where you come in
A 501(c)(4)'s IRS Form 990 is public and searchable through ProPublica's Nonprofit Explorer, though it discloses spending and grants, not the identity of individual donors. See how to look up who funds your representative for related lookups on the disclosed side of the system.
Related
Glossary: dark money · 501(c) distinctions · donor-advised fund
Sources
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"IRS targeting controversy," Wikipedia, citing Treasury Inspector General for Tax Administration report (2017), 2017. source ↩
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ProPublica, "How the IRS Gave Up Fighting Political Dark Money Groups," 2024. source ↩
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DeSmog, "The Friendly New Face of Dark Money: How Fidelity, Schwab, and Vanguard Helped Wealthy Donors Pour $171 Million of Dark Money into Project 2025," 2024. source ↩