Clinton family associate Sidney Blumenthal has made legal threats to the publisher of a forthcoming book featuring allegations against Democrats in connection with the Russia investigation in an attempt to stop publication, Fox News has learned.

A source familiar with the matter told Fox News that Blumenthal claimed the book – “The Plot Against the President: The True Story of How Congressman Devin Nunes Uncovered the Biggest Political Scandal in U.S. History,” by Lee Smith – was defamatory.

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“Blumenthal tried to stop it from being published,” the source told Fox News, saying the Hillary Clinton confidant sent threatening letters to Smith and publisher Center Street, a division of Hachette Book Group.

Fox News reached out to Blumenthal, who did not immediately respond.