Updated on December 19 at 9:30 a.m. EST

Bernie Sanders’s anger at the Democratic establishment is boiling over.

The senator from Vermont has promised he won’t run for the White House as an independent. But Sanders’s complicated and tense relationship with the Democratic Party is fast deteriorating. On Friday, Sanders’s campaign manager, Jeff Weaver, accused the Democratic National Committee of attacking “the heart and soul of our campaign” after the DNC moved to cut off the campaign’s access to key voter data. A few hours later, the campaign filed a lawsuit in federal court against the DNC, citing a breach of contract.

The DNC suspended access to the information after alleging that the Sanders campaign improperly accessed Hillary Clinton’s private campaign data. The Sanders campaign, in turn, blames the DNC and its data vendor for failing to properly secure the information and says it has already taken disciplinary action against one of its employees and that more may follow. The back-and-forth intensified Friday evening when Clinton campaign manager Robby Mook told reporters that the Sanders campaign had stolen data. “This breach is totally unacceptable and may have been a violation of the law,” Mook said.

As the ties that bind Sanders and the Democrats fray, the question arises: What would it take for the candidate to change his mind and break with the party?

America may soon find out. Backlash from the Sanders campaign was swift on Friday. “The leadership of the Democratic National Committee is now actively attempting to undermine our campaign,” Weaver said at a press conference. “This is unacceptable. Individual leaders of the DNC can support Hillary Clinton in any way they want, but they are not going to sabotage our campaign.”  

After a very public display of rancor, the Sanders campaign announced early Saturday morning that the DNC had agreed to restore access to the voter file. The campaign characterized the decision as an “about face,” adding that it was pleased “The DNC has reversed its outrageous decision.” DNC chair Debbie Wasserman Schultz tweeted: “now it’s time to refocus on winning in 2016.”

Voter data is critical for fundraising efforts, and losing access to the information delivered a major blow to Sanders’s presidential bid. It created a challenge for the campaign as it attempts to build momentum in the weeks leading up to the Iowa caucuses. The campaign’s lawsuit contends that not having access to the information could “significantly disadvantage, if not cripple, a Democratic candidate’s campaign for public office.”

Early on Friday, however, the DNC, showed no sign of backing down. “[The] Sanders campaign unfortunately doesn’t have anything other than bluster at the moment that they can put out there,” Wasserman Schultz told CNN. “This is not unreasonable ... It is the same decision that we would make if the shoe were on the other foot.”

Frustration has been building for months. Fewer Democratic primary debates have been scheduled than Republican debates, creating less of a chance for a presidential hopeful such as Sanders to knock Clinton out of the front-runner spot. The next Democratic debate is set to take place on Saturday, a time slot that has led to speculation among Sanders supporters that the Democratic establishment is actively trying to discourage viewership. It has also fed suspicion that the party is attempting to prematurely coronate Clinton. That fear is only intensifying as the fight between the Sanders campaign and the DNC escalates.

In a fundraising email sent to supporters on Friday, Weaver took issue with the handling of the Democratic debates. The DNC has put a “thumb on the scales in support of Hillary Clinton’s campaign,” Weaver said. “You see that fact evidenced in their decision to bury [t]he Democratic debates on weekends.”

“It’s more or less an open secret,” Weaver added.

Even as the dust appeared to settle, it was clear the conflict may not be over. In a statement released on Saturday,  the DNC announced that the Sanders campaign had agreed to comply with an ongoing investigation into the data breach.  Clinton spokesperson Brian Fallon urged swift follow through on “an independent audit.” Fallon added that the Clinton campaign “expect[s] further disciplinary action to be taken as appropriate.”

Clinton’s campaign responded to the incident on Friday, saying that it had been “informed that our proprietary data was breached by Sanders campaign staff.” A few hours later, Mook, the campaign manager, called for "a full accounting from the Sanders campaign of what their staff did" and proof that the “campaign no longer has access to our data” on a call with reporters.

"This is incredibly disappointing. This is someone who said he was going to run a different kind of campaign," Mook said.

The Republican establishment has long fretted that Donald Trump might mount an independent campaign for president, fracturing the party. Now, however, it’s a fight on the Democratic side that is on full display.