NYT:

Spurred by opposition to then-President Trump, donors and operatives allied with the Democratic Party embraced dark money with fresh zeal, pulling even with and, by some measures, surpassing Republicans in 2020 spending, according to a New York Times analysis of tax filings and other data.

The analysis shows that 15 of the most politically active nonprofit organizations that generally align with the Democratic Party spent more than $1.5 billion in 2020 — compared to roughly $900 million spent by a comparable sample of 15 of the most politically active groups aligned with the G.O.P….

A single, cryptically named entity that has served as a clearinghouse of undisclosed cash for the left, the Sixteen Thirty Fund, received mystery donations as large as $50 million and disseminated grants to more than 200 groups, while spending a total of $410 million in 2020 — more than the Democratic National Committee itself.

But nonprofits do not abide by the same transparency rules or donation limits as parties or campaigns — though they can underwrite many similar activities: advertising, polling, research, voter registration and mobilization and legal fights over voting rules.

The scale of secret spending is such that, even as small donors have become a potent force in politics, undisclosed money dwarfed the 2020 campaign fund-raising of President Biden (who raised a record $1 billion) and Mr. Trump (who raised more than $810 million)….

Here’s how we conducted our analysis.

The Times’s analysis of 2020 data is likely incomplete: Lax disclosure rules and the groups’ intentional opacity make a comprehensive assessment of secret money difficult, if not impossible. Nonprofits come and go, adapting to shifts in political power and tactics. Some exist in the gray space between philanthropy and politics, many transfer money back and forth, and some can remain hidden in unexamined tax filings for years.

Yet a number of strategists in both parties said their own understanding comported with The Times’s findings that the left eclipsed the right in politically oriented nonprofit spending and sophistication in 2020.