A former Democratic National Committee chair on Thursday revealed the existence of a previously secret agreement that appeared to confirm some of Bernie Sanders supporters’ fears about the 2016 Democratic primary.

Donna Brazile, a longtime Clinton ally who stepped in as DNC chair last year in the wake of Debbie Wasserman Schultz’s resignation, published an excerpt of her upcoming book in Politico in which she disclosed the details of a fundraising agreement between the DNC and the Clinton campaign reached in August 2015.

“The agreement — signed by Amy Dacey, the former CEO of the DNC, and [Clinton campaign manager] Robby Mook with a copy to [Clinton campaign counsel] Marc Elias— specified that in exchange for raising money and investing in the DNC, Hillary would control the party’s finances, strategy, and all the money raised,” Brazile wrote in the story under the headline “Inside Hillary Clinton’s Secret Takeover of the DNC.”

Brazile added of the deal: “[Clinton’s] campaign had the right of refusal of who would be the party communications director, and it would make final decisions on all the other staff. The DNC also was required to consult with the campaign about all other staffing, budgeting, data, analytics, and mailings.”

During the 2016 election, Sanders allies alleged that the DNC did not act as a neutral arbiter of the Democratic primary, favoring Clinton in its selection of debate times and fundraising. Their suspicions were only heightened when leaked emails published by WikiLeaks, and now reported to have been hacked by the Russians, appeared to show DNC staffers deriding Sanders and plotting ways to help Clinton. The accusations grew so heated that Wasserman Schultz resigned, which is when Brazile took over.

But now Brazile has provided explosive new evidence for the initial allegations. "The shocking news here is this idea they were exerting a level of control over DNC affairs that we didn't know about," said Kenneth Pennington, who served as digital director for the Sanders campaign. "If you had told me this during the primary — that they're using the joint fundraising committee to get veto power over DNC functions — I would have called you a conspiracy nut."

The debate over how the DNC acted has made Sanders supporters furious all over again. But though the revelations dredge up old tensions from the Democratic primary, they may also counterintuitively show that the party is trying to heal old wounds — and bring Sanders supporters into the fold.

What Brazile’s revelation is — and isn’t

There’s been a lot of confusion about the significance of Brazile’s allegations since her story was published. Brazile did not allege, as CNN reported in this chyron, that the DNC “robbed” Sanders of the nomination. She also did not claim to have been shocked by the existence of a fundraising agreement between Clinton and the DNC, since that agreement has been public for at least two years.

Instead, Brazile’s account is explosive for what it tells us — for the first time — about the nature of the fundraising agreement between Clinton and the DNC. What she charges is that the DNC, when starved for financial resources, agreed to trade a seemingly large part of its autonomy for Clinton’s help raising money — and that this agreement was inked in August 2015, long before voting in the 2016 Democratic primary had even begun.

Now, this deal does not guarantee that Sanders would have won the nomination without the obstruction of the DNC, as his supporters have long alleged. But it does at least suggest that Clinton’s team had veto power over some of the DNC’s decisions during the primary. Brazile writes that she concluded this was “proof” that Democrats tipped the nomination against Sanders, and that she told him about the agreement in a phone call before the general election. (Brazile herself had been implicated in tipping the scales of the primary after it was revealed she had given Clinton parts of debate questions ahead of time.)

“I had promised Bernie when I took the helm of the Democratic National Committee after the convention that I would get to the bottom of whether Hillary Clinton’s team had rigged the nomination process,” Brazile wrote. After discovering the document, she said, “I had found my proof and it broke my heart.”

A brief lesson in joint fundraising committees

The key to understanding Brazile’s conclusion and the current controversy is to understand the unusual fundraising apparatus at its center: the joint fundraising committee.

JFCs exist as a clever loophole to skirt existing campaign finance laws. Under current law, the most an individual donor can give to a presidential campaign committee is $2,700 per election. An individual donor can also give up to $33,400 to the DNC, and up to $10,000 to each state party committee.

But by existing as a group, the "joint committee" can get a big fat check that would be far too large for it to legally receive if its members were fundraising alone, according to Bob Biersack, a senior fellow at the Center for Responsive Politics. So a single donor could give around $353,000 to the Hillary Victory Fund, on the principle that money would go to the presidential committee, the DNC, and 32 state parties.

Now, the JFCs aren’t loved by campaign finance or good-government experts, but they’re not entirely out of the ordinary. Before his grassroots fundraising juggernaut took off, for instance, Sanders also had an agreement for a joint fundraising committee with the DNC. Donald Trump has a joint fundraising agreement with the Republican National Committee. They’re effective ways to tap donors who can give much more than $2,700.

And when Clinton’s JFC began, it appeared that all three parties involved had a great deal of mutual interest: Clinton would bring her big-money donors to the table, giving groups like the Democratic Party of Utah access to George Clooney’s wallet that it would never otherwise get. In exchange, Clinton could broaden her fundraising pitch by saying — as she did on several occasions — that she was raising money not just for herself but for the benefit of the entire Democratic Party.

But then it turned out that the money was not being shared between the three parties. Reporting by Politico showed that 99 percent of the money raised by the committee ended up going to the DNC or to Clinton's campaign directly. Some of the state party chairs objected — often anonymously, for fear of reprisal from national Democrats — but the DNC defended an agreement that appeared to starve it of resources and direct them almost entirely to Clinton’s team.

At the time, both Sanders and campaign finance experts thought Clinton was avoiding the spirit if not the letter of the law. "It's a circumvention of the contribution limits on the national party," Michael Malbin, executive director of the Campaign Finance Institute, told me at the time. "The victim here is anybody who thinks there's anything meaningful left to contribution limits."

But the document revealed by Brazile adds a new dimension to this story, suggesting that the Clinton team had control over the DNC throughout this fundraising process that cut out the state parties.

Some Democrats are trying to incorporate Sanders’s movement into the party’s mainstream

When news that Clinton’s joint fundraising money was mostly going back to her campaign emerged in 2016, Sanders alleged in a public debate that Clinton and the DNC had agreed to a “money laundering scheme.” And when Brazile’s story came out on Thursday, Sanders supporters were livid, with the senator’s former digital fundraising director tweeting that Bernie’s campaign was “right the entire time”: