Robert S. Mueller III in 2007. (Carlos Barria/Reuters)

This piece has been updated.

Martin Lederman teaches constitutional law at the Georgetown University Law Center and has twice served in the Office of Legal Counsel at the Justice Department.

The Justice Department has now confirmed that some of the senior officials involved in Robert S. Mueller III’s Russia investigation have ended their tenure with the special counsel or are planning to do so “in the near future.” It’s therefore increasingly fair to speculate that in the next few weeks or months Mueller may conclude his investigation and presumably transfer lead authority for continuing prosecutions to other Justice Department components.

A Justice Department regulation applicable to Mueller requires him to submit a report to Attorney General William P. Barr at the conclusion of his work “explaining [his] prosecution or declination decisions.” On Thursday, the House of Representatives passed a resolution, by a vote of 420 to 0, calling for that report to be released to Congress in “full” and to be released to the public, “except to the extent the public disclosure of any portion thereof is expressly prohibited by law.”

There appears to be a great deal of confidence that the Justice Department will comply with the House resolution: At least one publisher is even advertising for sale “The Mueller Report” — complete with an introduction by Alan Dershowitz, no less — and it’s already a bestseller on Amazon.

Those hoping or expecting to read that report, however, will likely be disappointed. It probably won’t see the light of day. That prospect, however, is not as troubling as it might seem, because the inordinate focus on Mueller’s closing report is misplaced. The document might be only one of three or more “reports” to emerge when the Russia investigation ends. The other reports, which will be submitted to Congress and parts of which may well become public, are likely to be far more revealing and more significant than what’s being called “the Mueller report.”

1. Mueller’s closing report to the attorney general

The relevant Justice Department regulation provides that Mueller’s report to Barr will be “confidential.” Barr therefore probably won’t share it with Congress, let alone the public at-large.

That doesn’t mean we won’t know most of the substance of that report: Mueller’s decisions to prosecute are reflected in the many grand jury indictments and other court filings that already are, or will be, publicly available. Those documents offer a rich and detailed story of Russian interference in our electoral system and the Americans who helped facilitate it or tried to thwart Mueller’s investigation. The only substantive pieces of Mueller’s report to Barr that won’t be transparent, then, are his explanations of why he chose not to seek indictments of others — possibly including the president.

For several good reasons, summarized in a 2000 Justice Department letter, such details about internal decision-making by prosecutors and prosecutorial “declinations” are rarely revealed, and Barr is unlikely to deviate from that practice.

To be sure, as the House resolution notes, the Justice Department has occasionally “provided investigatory information to Congress and the public concerning investigations of high-level public officials in both pending and closed cases.” In particular, the department will sometimes explain why it has concluded that sitting officials have not violated the law — as it did, for example, in special counsel John C.Danforth’s 2000 report regarding the Bureau of Alcohol, Tobacco and Firearms agents’ confrontation with Branch Davidians at Waco, Tex., and in a 2015 letter to Congress regarding the Internal Revenue Service’s treatment of tax exemption applications from nonprofit organizations.

To the extent Mueller has concluded that certain current federal officials, and perhaps others, have not acted illegally, it’s possible Barr will explain those decisions to Congress and the public. If he does so, however, it’s likely to be within the context of his own congressional report (see below), rather than by submitting Mueller’s report.

2. Barr’s notification to the congressional judiciary panels

The special counsel regulations require the attorney general himself to provide a “notification” to the leadership of the two congressional judiciary committees when Mueller’s investigation ends. As then-Attorney General Janet Reno explained when she promulgated the regulations 20 years ago, it’s this notification, rather than the special counsel’s report to the attorney general, that is designed to address “the interests of the public in being informed of and understanding the reasons for the actions of the Special Counsel.”

Barr’s notification might conceivably consist of only a brief outline explaining why Mueller closed up shop, which is all the regulation formally requires. That’s merely a floor, however, not a ceiling. The whole point of this notification requirement is (in Reno’s words) to “help ensure congressional and public confidence in the integrity of the process.” Barr was therefore right to promise senators that because “it is very important that the public and Congress be informed of the results of the special counsel’s work . . . my goal will be to provide as much transparency as I can consistent with the law.”

Barr might, for example, provide the judiciary committees with the sort of comprehensive “road map” of facts (accompanied by supporting evidence) that special prosecutor Leon Jaworski gave the House Judiciary Committee during the Watergate investigations — an account, likely drafted by Mueller himself, that would offer extensive and granular details of the evidence and perhaps of Mueller’s evaluative assessments of the evidence, too.

Of course, it’s possible such a road map would shine a harsh light on the president and others, thereby implicating the Justice Department’s traditional practice of trying to avoid unnecessarily sullying the reputations of persons who aren’t formally charged. That practice is not a hard-and-fast rule, however — there have been exceptions, particularly when, as here, Congress and the public have a compelling interest in understanding what current government officials have done and whether there’s an ongoing problem within the government that needs to be addressed.

The one thing we should not expect to see in Barr’s notification, however, is Mueller’s assessment about whether there are grounds to ask a grand jury to bring criminal charges against President Trump after he leaves office. The very reason the Office of Legal Counsel concluded (rightly or wrongly) that the Constitution forbids indictment of a sitting president is that such public charges would subject the president to the “stigma and opprobrium” of being branded an accused criminal without a timely opportunity to respond to his accusers in a court of law — a situation that (according to the opinion) might undermine the president’s “respect and stature both here and abroad,” and thus impact his ability “to act as the Nation’s leader in both the domestic and foreign spheres.” The same reasoning presumably would apply to a single prosecutor’s conclusion, not yet confirmed by a grand jury’s finding, of probable cause that the president has broken the law. (Indeed, such a public assessment of criminal culpability might taint the grand jury’s future consideration of the question, which is all the more reason Barr is unlikely to disclose it.)

Therefore, no matter how comprehensive Barr’s notification to the House and Senate Judiciary Committees might be, it would be surprising if it included any express conclusions about whether Trump’s conduct did or did not satisfy the elements of any particular criminal offenses. As long as Trump is in office, it will be up to the committees themselves — and Congress as a whole — to (in the words of the Jaworski road map) “determine what action may be warranted . . . by [the] evidence” presented in Barr’s notification.

3. The counterintelligence briefing to the Intelligence Committees

It’s important to keep in mind, however, that the Mueller report and Barr notification aren’t the whole ballgame — not by a long shot.

The public has understandably focused thus far on the special counsel’s prosecutorial decisions. Mueller was hired in the first instance, however, to superintend an ongoing FBI counterintelligence investigation. Although detection of crimes is often part of such an investigation, its principal function is not retrospective and punitive but forward-looking and preventive — to disrupt, or protect against, an ongoing foreign threat.

Mueller’s primary charge, in particular, is to ascertain the nature and extent of the Russian threat to the U.S. election system and any “links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump,” including, but not limited to, Trump himself.

This naturally includes assessing whether, how and to what extent Trump is compromised or is otherwise unable to perform his constitutional duties on behalf of the nation when it comes to matters involving Russia. What explains Trump’s sycophancy to Russian President Vladimir Putin in Helsinki and elsewhere, and Trump’s apparent willingness to believe whatever the Russian leader tells him, even when it contradicts the uniform assessments of his own intelligence agencies? His reluctance to criticize Putin’s regime, even for its assassinations abroad? His repeated efforts to distance himself from U.S. efforts to countermand Russia? His boasting to Russian officials that he’d removed James B. Comey as FBI director to take off the “great pressure” he faced “because of Russia”? Trump’s manifest disinterest in addressing the continuing threat to our electoral system? His persistent disparagement of the critically important Russia investigation as a “witch hunt”?

Does Trump have financial obligations to Russian interests? Was he — and does he continue to be — motivated by the prospects of a Moscow Trump Tower? Does Russian intelligence have kompromat on Trump that makes him susceptible to undue influence? Or is there a more benign explanation?

The counterintelligence investigation’s answers to these and similar questions — especially its possible assessment of the president’s capacity to address the foreign threat — are of far greater current importance to the functioning of our government than determining whether Trump’s deeply inappropriate conduct in 2016-2017 violated any particular criminal statutes.

The first and primary audiences for the results of an FBI counterintelligence investigation are, not surprisingly, the components of the intelligence community responsible for disrupting and protecting against the identified threat. In addition, however, the FBI has a legal obligation to “keep the congressional intelligence committees fully and currently informed” of the fruits of such an investigation.

Determining precisely what it means to “fully and currently inform” the committees is something that’s been worked out over many years, outside the public eye, between the intelligence components of the executive branch and the congressional intelligence committees. In some cases, it consists of only an oral briefing, but occasionally there are written submissions, as well.

Whatever the historical practice has been, it’s virtually certain in this case that Barr, Mueller and the FBI will, at a minimum, inform the intelligence committees about whatever evidence Muller has collected concerning whether Trump is compromised with respect to Russia and, if so, in what way and to what effect. Mueller’s general conclusions on those questions, and at least an outline of the evidence supporting them, aren’t the sorts of things the Justice Department realistically could or should omit in its required reporting.

At that point, it will primarily be the responsibility of the chairs of the committees — Richard Burr (R-N.C.) in the Senate and Adam B. Schiff (D-Calif.) in the House — to assess how much of the information they can share with the rest of Congress and the public. This isn’t something that’s commonly done with the results of counterintelligence investigations, for obvious reasons: In the ordinary case, much of the information is classified, because it could reveal sensitive sources or methods and because there’s an interest in not revealing to the foreign subjects of the investigation what our government has learned about their activities.

This isn’t remotely an ordinary case, however. Congress and the public have a critical need to know whether and to what extent the president is compromised and whether he is fit to respond to the Russian threat without fear or favor. It’s therefore safe to assume Mueller will try to convey such information in a form that permits the greatest possible dissemination, consistent with national security imperatives.

Read more:

The Post’s View: A note to Barr and Whitaker: The Mueller report must be made public

Lowell Weicker: I was on the Watergate committee. Don’t hide Mueller’s report from the people.

Philip Zelikow: What Robert Mueller and William Barr need to tell us

Marc A. Thiessen: The Mueller probe could turn out to be a disaster — for the Democrats