The hacking spree that upended the presidential election wasn’t limited to Democratic National Committee memos and Clinton-aide emails posted on websites. The hacker also privately sent Democratic voter-turnout analyses to a Republican political operative in Florida named Aaron Nevins.

Learning that hacker “Guccifer 2.0” had tapped into a Democratic committee that helps House candidates, Mr. Nevins wrote to the hacker to say: “Feel free to send any Florida based information.”

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