The National Republican Senatorial Committee (NRSC) is the source of the leak that brought down Sen. John Walsh (D-Mont.), its director said at an event on Thursday.

An NRSC researcher discovered that Walsh had plagiarized large portions of his masters thesis at the Army War College. The group provided the evidence to The New York Times, which broke the story in July along with a graphic detailing the extent of the plagiarism.

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Walsh dropped out of the race and his degree was later revoked by the institution.

Democrats were left with little time to find a new candidate. They replaced Walsh, who had taken over the seat when former Sen. Max Baucus (D-Mont.) was named ambassador to China, with state legislator and math teacher Amanda Curtis. She currently trails her Republican opponent, Rep. Steve DainesSteven (Steve) David DainesTax bill raises red flags for Senate GOP Overnight Energy: EPA kicking scientists who get grants off advisory boards High stakes as Trump heads to Hill MORE.

NRSC Executive Director Rob Collins said at the Tuesday event that the group was also behind the release of an internal strategy memo from Michelle Nunn’s campaign that embarrassingly detailed her own perceived vulnerabilities. The release of the memo briefly put a dent in Nunn’s Georgia Senate campaign.

The NRSC which found the Google Document online sat on it for seven months before leaking it to the conservative National Review.

This election cycle has seen a bumper crop of new opposition research groups that look to give campaigns ammunition for attack ads — and will likely play a role in the 2016 presidential campaign.

The research groups have paid for so-called trackers to follow candidates around, recording their every move.

Sometimes, the hunger for opposition research can backfire.

When the left-leaning American Bridge distributed a video that appeared to show the Georgia Republican Senate candidate David Purdue signing the torso of a young woman, it was revealed that he had only been signing her diabetic insulin pump.

The group later took the video down.