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Associated Press

WASHINGTON — The presidential campaign of Vermont Sen. Bernie Sanders angrily accused the Democratic National Committee of trying to "undermine our campaign" by barring it from a voter database after a breach enabled his staff to improperly access information compiled by rival Hillary Clinton's campaign.

"Clearly, in this case, they are trying to help the Clinton campaign," Sanders campaign manager Jeff Weaver said.

DNC Chairwoman Debbie Wasserman Schultz responded that once the committee became aware "that the Sanders campaign had inappropriately and systematically accessed Clinton campaign data," it directed its vendor to suspend Sanders' campaign access to the information.

A summary of computer logs shows that four aides to Sanders' presidential campaign accessed proprietary voter data compiled by Clinton's campaign and some of the aides saved the voter information, according to a person familiar with the data logs and the breach.

The person said the data represented millions of dollars invested by the Clinton campaign. The person was not authorized to speak publicly and spoke on condition of anonymity.

The Sanders campaign fired one staff member but blamed the vendor who runs the DNC's voter database for making "serious errors."

Weaver said four members of the Sanders campaign had accessed the information but that only the actions of one, the campaign's data director, had risen to the level of a fireable offense.

The DNC maintains an extensive list of voter information, which it rents to campaigns and which updates with their own data. The data allows campaigns to target likely voters and anticipate what issues might motivate them to support a candidate.

It remained unclear how long the Sanders campaign would be barred from the DNC database, but Weaver threatened to file a federal lawsuit later Friday if the DNC did not immediately restore its access.

The information could be crucial in the Sanders campaign's ability to identify and persuade voters in the kickoff February contests of Iowa and New Hampshire. Sanders has built a strong following among young voters and liberals, but Clinton has maintained a lead in national polls.