Apparently Mueller took exception to Barr's 4 page letter that provided the Mueller Dossier's principal conclusions. Barr initially issued that letter shortly after receiving the Dossier--he wanted Barr to also release the executive summaries from the Dossier. Barr's position was simple: he issued his four page letter to fulfill the reporting requirements in the regulations. He did not agree with Mueller's idea of a partial release of the Dossier, preferring to release the entire document as a whole, with necessary redactions. That was exactly what Barr did.
Here is a key passage from the WaPo article:
A day after Mueller sent his letter to Barr, the two men spoke by phone for about 15 minutes, according to law enforcement officials.
In that call, Mueller said he was concerned that media coverage of the obstruction investigation was misguided and creating public misunderstandings about the office’s work, according to Justice Department officials. Mueller did not express similar concerns about the public discussion of the investigation of Russia’s election interference, the officials said. Barr has testified previously he did not know whether Mueller supported his conclusion on obstruction.
When Barr pressed Mueller on whether he thought Barr’s memo to Congress was inaccurate, Mueller said he did not but felt that the media coverage of it was misinterpreting the investigation, officials said.
In their call, Barr also took issue with Mueller calling his memo a “summary,” saying he had never intended to summarize the voluminous report, but instead provide an account of its top conclusions, officials said.
Justice Department officials said that, in some ways, the phone conversation was more cordial than the letter that preceded it, but that the two men did express some differences of opinion about how to proceed.
Barr said he did not want to put out pieces of the report, but rather issue the document all at once with redactions, and that he didn’t want to change course, according to officials. Barr also gave Mueller his personal phone number and told him to call if he had future concerns, officials said.
Throughout the conversation, Mueller’s main worry was that the public was not getting an accurate understanding of the obstruction investigation, officials said.
“After the Attorney General received Special Counsel Mueller’s letter, he called him to discuss it,” a Justice Department spokeswoman said Tuesday evening. “In a cordial and professional conversation, the Special Counsel emphasized that nothing in the Attorney General’s March 24 letter was inaccurate or misleading.
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.
“However, the Attorney General ultimately determined that it would not be productive to release the report in piecemeal fashion,” the spokeswoman said.
“The Attorney General and the Special Counsel agreed to get the full report out with necessary redactions as expeditiously as possible. The next day, the Attorney General sent a letter to Congress reiterating that his March 24 letter was not intended to be a summary of the report, but instead only stated the Special Counsel’s principal conclusions, and volunteered to testify before both Senate and House Judiciary Committees on May 1 and 2.”
Some senior Justice Department officials were frustrated by Mueller’s complaints because they had expected that the report would reach them with proposed redactions, but it did not. Even when Mueller sent along his suggested redactions, those covered only a few areas of protected information, and the documents required further review, these people said.
The Washington Post and the New York Times had previously reported some members of Mueller’s team were frustrated with Barr’s characterization of their work, though Mueller’s own attitude was unknown before now.
As Barr stated before, Mueller is not the AG. He was a prosecutor working for the AG and the AG makes the calls on how to handle the Dossier. As far as the obstruction portion of the Dossier was concerned, the top officials at DoJ judged Mueller's theory to be legally deficient and that it failed to lay out evidence of obstruction. Barr gets paid to make those decisions, and his decision was made on long established principles of law, rather than tendentious and frivilous theories designed only to harass the president.
In the end, Mueller was forced to admit that "nothing in the Attorney General’s March 24 letter was inaccurate or misleading." In the event, essentially the entire report was shortly released. End of story. I expect Barr to be unapologetic tomorrow.
UPDATE 1: The WSJ is reporting that Barr will defend his treatment of Mr. Mueller’s findings and his determination that Mr. Trump didn’t obstruct justice in prepared remarks that were made available.
“The Special Counsel regulations provide for the report to remain confidential. Given the extraordinary public interest in this investigation, however, I determined that it was necessary to make as much of it public as I could, it would have been inappropriate to release details of the special counsel’s obstruction case without making a judgment as to whether the president committed a crime.”
“Although we disagreed with some of the Special Counsel’s legal theories and felt that some of the episodes examined did not amount to obstruction as a matter of law, we accepted the Special Counsel’s legal framework for purposes of our analysis and evaluated the evidence as presented by the Special Counsel in reaching our conclusion.”
As far as Mueller's claim that "media coverage of the obstruction investigation was misguided and creating public misunderstandings about the office’s work", the truth is simply this: Mueller's Dossier itself created misunderstanding because it failed to reach any principled conclusion--but insinuated that there was a legitimate case that could be handled politically. That's not a call for a prosecutor to make. Barr therefore made the prosecutor's call: there was no obstruction case under established principles of law. In other words, Barr provided the necessary guidance to prevent the politically motivated misunderstandings that Mueller intended should arise from Mueller's Dossier misrepresentation of the well settled principles of the law on obstruction. Congress can do what Congress wants, but the law is clear.