The top Republican investigating the 2012 Benghazi attacks accused his Democratic counterpart of mounting a strategic, two-year effort to stop the probe and discredit Republicans’ work as a favor to presumptive Democratic presidential nominee Hillary Clinton.

Rep. Trey Gowdy (R-S.C.), chairman of the House Select Committee on Benghazi, questioned the motives of ranking member Elijah Cummings (D-Md.) in a biting, sarcastic letter after Cummings asked to participate in writing the panel’s final investigative report.

“If it were true the Majority has found ‘nothing new’ and ‘gained no additional insight,’ it makes little sense for the Minority to suddenly be interested in the Committee’s report,” Gowdy wrote in the letter. “Moreover, you have spent far more time writing letters, selectively leaking material, and spreading mischaracterizations than you have actually participating in this investigation.”

Gowdy said Dems will “have the opportunity to review the report and offer changes in a manner consistent with the rules of the House.” He did not elaborate on when he will announce a mark-up, or whether Democrats will have access to drafts before the mark-up stage.

“It appears that the Republicans have decided not to vet their draft report for accuracy with the rest of the Select Committee Members before they release it to the public shortly before the political conventions this summer,” Democratic committee spokesman Paul Bell said in a statement. “After more than two years and nearly $7 million in taxpayer funds, this kind of report won’t be taken seriously and will be widely dismissed as the obvious partisan political attack that it is.”

The letter represents the latest salvo between panel Republicans and Democrats, whose intense mutual suspicion has made the Benghazi committee one of Congress’s most dysfunctional panels.

After two years of controversy and partisan struggle, communication between the two sides has come to rely on scathing letters full of accusation and grievance. They are almost always made public.

“The very essence of your two-year obstruction has been impeached,” Gowdy wrote in the latest example.

“This investigation has uncovered new information that will change how the public views what happened before, during, and after the attacks in Benghazi. Despite your best efforts to prevent it from happening, actually talking to eyewitnesses and actually accessing relevant documents has produced new information. Sadly, if you had helped even a little bit we could have accessed this information sooner.”

Gowdy has been under pressure from critics for months to conclude his investigation. He has promised to release the final report before the party nominating conventions in late July and blames obstruction by the Obama administration for how long the probe has taken.

At one point, Gowdy zeroed in on Cummings’s support for Clinton in the investigation. The Maryland Democrat has also endorsed her in the presidential race.

“Several news outlets have taken note of your focus on acting as the former Secretary’s ‘defense attorney,’  ‘chief defender,’  ‘top supporter,’  ‘staunch defender,’  and ‘biggest defender,'” Gowdy wrote. “This is why I was particularly struck by the Minority’s claim this week it is finally ready to ‘put politics aside,’ especially in light of its assertion last month this Committee has ‘lost any semblance of credibility.'”

Bell argued Republicans inflicted damage on themselves in the way they approached the investigation.

“Democrats are deeply disappointed that Republicans have rejected virtually every opportunity to make this investigation bipartisan, fact-based, and credible,” he stated.