As noted, while the book by Aaron Zebley et al does not reveal a single new detail from the Russian investigation, it provided a bunch of new details on discussions between Mueller’s team, Trump’s lawyers, and DOJ. Two chapters focus almost entirely on discussions about an interview and, after Trump’s new legal team in May 2018, reversed earlier assurances Trump would sit for an interview, discussions about a subpoena.

The book describes how, after getting nowhere with requests for a voluntary interview, Zebley approached Scott Schools (then the senior non-political appointment at DOJ) about subpoenaing Trump. Schools asked for a memo making the case.

Three days after Mueller delivered it, Schools left DOJ.

Bob’s May 16 letter about the importance of an interview did not get an immediate response from Trump’s lawyers. Instead, after a series of emails, calls, and meetings during the ensuing weeks, the Raskins told us that they would agree to an interview on preelection Russia-related topics only. There could be no questions on obstruction. Bob rejected this proposal.

By the end of June, it was becoming clear that a subpoena might be the only way to secure the president’s testimony on obstruction. Aaron called Schools at the DOJ and relayed the president’s latest position. Aaron explained that “evidence from the president is likely to be of significant value to our evaluation of the issues.”

Schools did not immediately respond, so Aaron continued: “If we can’t negotiate a resolution, we’d like to point to a subpoena as our next step.” Aaron told Schools we wanted the department to agree to enforce a subpoena in the courts, including the Supreme Court if it came to that. “We have written materials that go through the evidence and our analysis” as to why a subpoena was necessary and appropriate, Aaron said.

Schools responded in his muted southern drawl, “Think we’ll want to see those.”

Four days later, on July 3, we delivered to Schools and O’Callaghan a memo, “Preliminary Assessment of Obstruction Evidence,” with a set of supporting documents. The takeaway was on page 1: the president had refused an interview; we had gathered significant evidence on obstruction and had determined that the law enabled us to compel the president’s testimony; and, finally, “we have concluded that the issuance of a subpoena is justified.” There was no immediate response from the department. (On July 6, 2018, after a decades-long career at the Department of Justice, Schools left to take a job in the private sector.)

There’s no evidence, here, that the memo was the reason Schools left, apparently with no notice to Mueller’s team.

But eight months later, in advance of the first meeting between Mueller and Barr, Ed O’Callaghan probed what would appear in the report on obstruction.

He specifically referred to the memo justifying the subpoena as “aggressive.”

We knew that one of the main issues for our March 5 meeting with Barr would be obstruction of justice. In the days leading up to the meeting, O’Callaghan had asked Aaron how we planned to handle our obstruction findings. “Will your report be as aggressive as your legal analysis from last summer?” he asked, referring to the memo we submitted in July 2018 about a subpoena for the president’s testimony. “That is a topic we want to discuss.”

As it happens, almost immediately after Mueller gave DOJ the memo in June 2018, according to files released under FOIA, they pulled in Office of Legal Counsel and (at least for a few meetings), National Security Division. It’s not entirely clear Mueller’s team realized Rod Rosenstein’s people were doing that.