The seats that Guccifer 2.0 targeted in the document dumps were hardly random: They were some of the most competitive House races in the country. In Ms. Taddeo’s district, the House seat is held by a Republican, even though the district leans Democratic and Mrs. Clinton won it this year by a large majority.

To prepare for the race, the D.C.C.C. had done candid evaluations of the two candidates vying in the primary for the nomination. Those inside documents, bluntly describing each candidate’s weaknesses, are considered routine research inside political campaigns. But suddenly they were being aired in public.

Ms. Taddeo, one of the internal D.C.C.C. documents noted, had “proven to be a somewhat poor fund-raiser and she has gained a reputation as an inadequate campaigner among some of the talkers in the community.”

Her Democratic opponent in the August primary, Joe Garcia, “also made a large misstep during the campaign saying ‘communism works,’ which did not sit well in an area with a large Cuban refugee population,” the document says. “More embarrassingly, Garcia was caught on a C-Span feed picking his earwax and seemingly eating it, and the video made the rounds on the internet.”

Mr. Garcia was the first to use the material as a tool to attack his opponent, showing up at a televised debate with a printout of the documents and accusing Ms. Taddeo of hiring a private detective to follow him, an allegation she disputed. It was the first of many attacks based on the leaked material.

After Mr. Garcia defeated Ms. Taddeo in the primary using the material unearthed in the hacking, the National Republican Campaign Committee and a second Republican group with ties to the House speaker, Paul Ryan, turned to the hacked material to attack him.

In Florida, Guccifer 2.0’s most important partner was an obscure political website run by an anonymous blogger called HelloFLA!, run by a former Florida legislative aide turned Republican lobbyist. The blogger sent direct messages via Twitter to Guccifer 2.0 asking for copies of any additional Florida documents.