The Democratic primary has taken a nasty turn ahead of the big debate

Two months ago, at the first Democratic primary debate, Sen. Bernie Sanders (I-Vermont) provided the most memorable moment of the night when he defended front-runner Hillary Clinton on the biggest controversy of her campaign.

"Let me say something that may not be great politics," Sanders said. "I think that the secretary is right."

He thundered: "The American people are sick and tired of hearing about your damn emails!"

Don't expect such a moment Saturday night.

Clinton, the former secretary of state, and Sanders are set to battle in a potentially pugnacious primary debate, one day after their campaigns erupted in a fierce back and forth that both sides tried to use to their advantage. The Democratic primary campaign has become more personal than ever, less than two months before the first votes are cast.

The debate is set to begin at 8 p.m. ET in Manchester, New Hampshire. Former Maryland Gov. Martin O'Malley (D) will join Clinton and Sanders on stage.

The Granite State and its first-in-the-nation primary has long been viewed as a crucial state for Sanders, whose insurgency in the race has shocked the Democratic establishment. According to a Real Clear Politics average of recent New Hampshire surveys, Sanders leads Clinton, 48% to 43.8%. O'Malley grabs 3.5% of the vote.

The debate comes at a time when tensions are higher than ever before in what has, to this point, been a mostly civil campaign. The Sanders campaign took the unprecedented step of filing a lawsuit against the Democratic National Committee on Friday, after the DNC had suspended the Sanders campaign's access to key voter data.

The DNC had revoked the Sanders campaign's access after it was revealed that a Sanders staffer improperly gained access to Clinton campaign voter files. But in the lawsuit, the Sanders campaign accused the DNC of overreaction and of working to protect Clinton while "actively undermin[ing]" Sanders' bid.

"By their action, the leadership of the Democratic National Committee is now actively attempting to undermine our campaign. This is unacceptable," campaign manager Jeff Weaver said in an earlier, hastily scheduled press conference.

"Individual leaders of the DNC can support Hillary Clinton in any way they want. But they are not going to sabotage our campaign, one of the strongest grassroots campaigns in modern history. We are announcing today that if the DNC continues to hold our data hostage and continues to try to attack the heart and soul of our grassroots campaign, we will be in federal court this afternoon seeking immediate relief."

A summary of computer logs showed that four aides to Sanders' campaign accessed voter data compiled by Clinton's campaign, according to The Associated Press. Some of the aides reportedly saved the information. The Clinton campaign said its data was breached by the Sanders campaign in "25 searches by four different accounts," and that the data was saved into the Sanders campaign's account.

"This breach is totally unacceptable and may have been a violation of the law," Clinton campaign manager Robby Mook said in a conference call with reporters Friday evening.

"We are particularly disturbed right now that they are using the fact that they stole data as a reason to raise money for their campaign," he added. "And I would certainly hope that they would stop trying to make money off of what they did, stop politicizing and work to make sure that what took place is remedied."

Late Friday night, the Sanders campaign and DNC came to a deal in which the campaign would regain access to voter information Saturday morning.

In a statement, the Sanders campaign said the Democratic National Committee "capitulated" in the face of its lawsuit.

"We are extremely pleased that the DNC has reversed its outrageous decision to take Sen. Sanders' data. The information we provided tonight is essentially the same information we already sent them by email on Thursday," said Jeff Weaver, Sanders' campaign manager, in a statement.

He added: "Clearly, they were concerned about their prospects in court."

The Sanders campaign said access to the database should be restored by early Saturday morning. It claimed that more than 500,000 people signed online petitions in support of the Sanders campaign Friday.

In a statement early Saturday morning, DNC Chair and Rep. Debbie Wasserman Schultz (D-Florida) said: "The Sanders campaign has now complied with the DNC's request to provide the information that we have requested of them. Based on this information, we are restoring the Sanders campaign's access to the voter file, but will continue to investigate to ensure that the data that was inappropriately accessed has been deleted and is no longer in possession of the Sanders campaign."

"The Sanders campaign has agreed to fully cooperate with the continuing DNC investigation of this breach," she continued. "The fact that data was accessed inappropriately is completely unacceptable, and the DNC expects each campaign to operate with integrity going forward with respect to the voter file."