Robert Mueller in 2013. (Brendan Smialowski/AFP/Getty Images)

Nelson W. Cunningham has served as a federal prosecutor in the Southern District of New York, general counsel of the Senate Judiciary Committee and general counsel of the White House Office of Administration.

Recently, Sen. Robert P. Casey Jr. (D-Pa.) expressed the view of many in Washington regarding the Trump administration and foreign influences: “I don’t think we’ll know anywhere near the full story until [special counsel Robert S. Mueller III] issues his report.”

That is, if we ever see a Mueller report.

Twenty years ago, independent counsel Kenneth Starr concluded his years-long investigation of President Bill Clinton with a 211-page report detailing — in famously explicit detail — the president’s affair with Monica Lewinsky. Starr submitted his report (and six volumes of supporting evidence) to the House of Representatives as “substantial and credible information that President William Jefferson Clinton committed acts that may constitute grounds for an impeachment.” His report hit the top of the bestseller lists.

Opinion | If President Trump were to fire the bane of his legal troubles, he could spark a legal and constitutional crisis. Post Opinion writer Quinta Jurecic lays out how Trump could get rid of special counsel Robert Mueller, and what would happen as a result. (Adriana Usero/The Washington Post)

As the media and the public avidly follow the slow reveal of the Mueller investigation, there is a widespread assumption that Mueller will pull it all together into a Starr-like summary.

But there are substantial legal barriers to a “Mueller Report,” at least one that would see the light of day.

First, special counsel Mueller is not independent counsel Starr. They were appointed under different authorities, with radically different rules for reporting and disclosure. Starr was required by the independent counsel statute governing his appointment not only to conduct a criminal investigation but also to submit a report to Congress if he found any evidence of impeachable offenses.

However, that statute expired in 1999. Mueller was appointed under the far narrower Justice Department regulation for special counsels that replaced the independent counsel statute. Far from requiring a report to Congress of impeachable offenses, these regulations tightly circumscribe Mueller’s ability to do so.

Section 600.8(c) of the regulations provides that the special counsel shall provide the attorney general with a “confidential report explaining the prosecution or declination decisions reached by the Special Counsel.” If the special counsel finds that “other governmental action outside the criminal justice system might be appropriate,” (presumably, such as impeachment) he is empowered only to “consult with the Attorney General with respect to the appropriate component to take any necessary action.”

How much of the special counsel’s “confidential” report on prosecution or declination decisions, or consultations an impeachment recommendation, might come to light? The regulations provide that the attorney general may release the special counsel’s report if he finds it would “be in the public interest.” But nothing requires him to do so. Moreover, any release must “comply with applicable legal restrictions,” which pose substantial barriers.

The only disclosure the attorney general is required to make, to the chairs and ranking members of the House and Senate judiciary committees, is if he concludes that “a proposed action by a Special Counsel was so inappropriate or unwarranted under established Departmental practices that it should not be pursued.”

The Post’s Sari Horwitz and Marc Fisher compare the events of special counsel Robert Mueller’s life to how he's portrayed in pop culture. (Sarah Parnass/The Washington Post)

As for Mueller, the regulations forbid him from publicly discussing his findings except as “governed by the generally applicable Departmental guidelines concerning public comment with respect to any criminal investigation” — which generally forbid public comment on closed investigations. (Remember, it was James B. Comey’s unorthodox news conference in the Hillary Clinton email matter that initially formed the basis for his termination as FBI director).

So while Starr was required by statute to forward any findings of impeachable offenses to Congress, Mueller is forbidden to speak publicly and may only forward a “confidential report” to the attorney general (or, in this case, Deputy Attorney General Rod J. Rosenstein). While Rosenstein may feel obliged to make a limited disclosure to Congress of any disagreement with Mueller, there is no formal mechanism to transmit Mueller’s conclusions regarding impeachable offenses, much less the underlying evidence, to the Congress.

Moreover, even if Rosenstein wanted to pass Mueller’s report to Congress or to the public, it is not clear that he could. Much of Mueller’s evidence would have been gathered via the grand jury — and Rule 6(e) of the Rules of Criminal Procedure forbids the public release of grand-jury material, with no applicable exceptions. A report that excluded the underlying grand-jury material would include only a sliver of allegations.

There is court precedent to suggest that grand-jury materials may properly be released to a congressional committee in support of impeachment proceedings. Leon Jaworski, the special prosecutor for the Watergate scandal, was able to forward his grand jury’s report and evidence to the House Judiciary Committee. But in that case, the committee majority wanted the evidence, had subpoenaed it, and President Richard Nixon expressed no objection. There is little to suggest that the current committee majorities would diligently and swiftly pursue the release of information harmful to the sitting president, who could hardly be expected to express no objection.

Finally, as if the procedural and political barriers to release of a Mueller report were not enough, don’t forget that much of what Mueller has gathered is highly classified — FISA warrants, NSA intercepts, evidence obtained from intelligence agencies. While Rosenstein might make disclosures to cleared members of Congress and their staffs, any public release would be surely be so heavily redacted as to be [redacted].

Mueller is surely aware of the many difficulties he will face in putting forward a comprehensive report. Perhaps that is why he has begun laying out his case in lengthy indictments, as he did recently against 13 Russians who are unlikely ever to be arrested or tried. Justice may never be served against them, but we learned a great deal about Mueller’s findings from the indictment.

Recent events suggest that Mueller and his high-powered team may be moving into the final stages of their investigation. They have obtained a plea and cooperation from Donald Trump’s deputy campaign manager, Rick Gates, and pressure is mounting on former campaign chairman Paul Manafort to do the same. Mueller is reportedly negotiating the terms under which he might interview President Trump — surely the final major step.

Mueller may soon lay out his final markers — perhaps further indictments, perhaps a full report to Rosenstein. But the questions of whether Congress will see his final report, or whether the public will ever be able to see it, remain very much open. At the very least, we may expect extended and complex court proceedings to try to delay release past November’s midterm elections. The public and the press should brace themselves. And members of Congress should begin speaking out.