Special Counsel Robert Mueller wrote a letter to Attorney General William Barr complaining about how he “publicized” the conclusions of his investigation in summaries to Congress before the full report was publicly released.

Barr’s spin did not “fully capture” the probe into Russian meddling in the 2016 election and potential links to the Trump campaign or the results of that investigation, Mueller wrote, adding that the summary has sowed “public confusion” about what the probe found.

Disclosure of the rebuke was made Tuesday night on the eve of Barr’s testimony before the Senate Judiciary Committee and drew instant criticism from Democrats.

Sen. Amy Klobuchar, who sits on the committee, said in a tweet that she was revising her questions for the attorney general, while others called on Barr to resign to or face impeachment.

Mueller fired off the letter to Barr on March 27, just three days after the attorney general sent his Mueller Report summary to Congress. A Justice Department official confirmed the letter to The Daily Beast, which was first reported by The Washington Post.

That summary, Mueller wrote, “did not fully capture the context, nature, and substance of this office’s work and conclusions,” according to the Post.

“There is now public confusion about critical aspects of the results of our investigation,” he continued. “This threatens to undermine a central purpose for which the Department appointed the Special Counsel: to assure full public confidence in the outcome of the investigations.”

The letter also requested Barr release the report’s “introductions and executive summaries,” in order to “alleviate the misunderstandings that have arisen” among the public and Congress about the probe.

In the summaries Barr sent to Congress, he wrote that Mueller and his team found no collusion between Russia and the Trump campaign to influence the election and “did not draw a conclusion—one way or the other” on the question of whether President Trump had obstructed justice. Barr said his office had determined the report did not outline actions that could support an obstruction charge.

After Barr got the letter, he called Mueller to discuss it, the Justice Department confirmed.

“In a cordial and professional conversation, the Special Counsel emphasized that nothing in the Attorney General’s March 24 letter was inaccurate or misleading,” DOJ said in a statement. “But, he expressed frustration over the lack of context and the resulting media coverage regarding the Special Counsel’s obstruction analysis. They then discussed whether additional context from the report would be helpful and could be quickly released.”

In the end, DOJ said, the two men decided that the full report should be released in one fell swoop rather than piecemeal.

Shortly before he released the full report in mid-April, Barr held a press conference where he said he disagreed with some of Mueller’s legal theories on the question of obstruction of justice.

His testimony Wednesday before the Judiciary Committee will mark the first time lawmakers have a chance to question Barr about the report since its release.