The Sanders Campaign and Clinton's Voter Data

The presidential candidate tangled with the Democratic National Committee Friday over a data breach.

Manuel Balce Ceneta / AP

Updated on December 18 at 5:44 p.m. EST

The Bernie Sanders campaign came out swinging against the Democratic National Committee’s decision to suspend its access to the list of likely Democratic voters after the campaign was accused of improperly accessing Hillary Clinton’s private campaign data.

“We are announcing today if the DNC continues to hold our data hostage and continues to attack the heart and soul of our grassroots campaign, we will be in federal court this afternoon seeking immediate relief,” Jeff Weaver, Sanders’s campaign manager, said at a news conference. “What is required here is a full and independent audit of the DNC’s mishandling of this data, and its security from the beginning of this campaign to the present.”

Weaver followed through on that promise: the presidential campaign filed a lawsuit against the Democratic National Committee Friday night, the Associated Press reported.

Weaver laid the blame squarely at the hands of NGP VAN, the vendor that handles the master file, and the DNC. He said the campaign discovered a similar breach in October, segregated the data, and informed the DNC of the breach. He said the DNC assured the campaign that the problem would be fixed.

“But apparently, they are not competent in maintaining the security of data between the campaigns,” he said.

The Washington Post reported Friday that a low-level staffer viewed the information. Weaver told the Post a staffer was fired over the incident. But The New York Times reported, citing three people with direct knowledge of the breach, that four user accounts associated with Sanders’s campaign ran searches while Clinton’s data was breached. At the news conference, Weaver said the campaign was speaking to other staffers “and further disciplinary action may follow.”

The Post adds:

The DNC maintains the master list and rents it to national and state campaigns, which then add their own, proprietary information gathered by field workers and volunteers. Firewalls are supposed to prevent campaigns from viewing data gathered by their rivals.

NGP VAN, the vendor that handles the master file, said the incident occurred Wednesday while a patch was being applied to the software. The process briefly opened a window into proprietary information from other campaigns, said the company’s chief, Stu Trevelyan. He said a full audit will be conducted.

The Sanders campaign has been told it will only be granted access to the list when it provides both an explanation for what happened, as well as assurances that Clinton’s data has been destroyed, the Post added.

The suspension of access is a blow to the Sanders campaign. Clinton, the former secretary of state, is leading Sanders, the senator from Vermont, in polls for the Democratic presidential nomination. On Thursday, the Sanders campaign received the endorsement of the Communications Workers of America, a major union. The two candidates face off in the Democratic debate on Saturday.

Weaver, speaking to the Post, and the Times, citing the DNC, attributed blame for the software glitch to NGP VAN, whose chief executive called it an “isolated incident.”