Julian Zelizer is a professor of history and public affairs at Princeton University, and author, with Kevin Kruse, of the new book " Fault Lines: A History of the United States Since 1974 ." Michael Zeldin, a CNN legal analyst, served as Deputy Independent Counsel, and later as Independent Counsel, in the investigation into allegations that the administration of George H. W. Bush violated the privacy rights of candidate Bill Clinton in the 1992 presidential campaign. He also served as a Special Counsel to Robert Mueller in the Department of Justice. The opinions expressed in this commentary are those of the authors; view more opinion articles on CNN.

(CNN) When Robert Mueller delivers his final report to the Justice Department, he will be constrained from what he can say because of the Special Counsel regulations that govern his appointment.

Mueller, like all special prosecutors since 1999, lives in the shadow of Congress's response to the report filed by Independent Counsel Kenneth Starr in the Monica Lewinsky matter. That is, in light of the perceived problem of independent prosecutors functioning with little supervision as well as the legal obligation to file a public report, Congress allowed the Independent Counsel Act to expire.

This problem dates back to September 9, 1998, when Kenneth Starr submitted what, by some, was considered to be an unnecessarily salacious report to the House Judiciary Committee concerning his investigation into President Clinton's relationship with White House intern Monica Lewinsky.

The Independent Counsel law required Starr to: "... advise the House of Representatives of any substantial and credible information which such independent counsel receives, in carrying out the independent counsel's responsibilities under this chapter, that may constitute grounds for an impeachment." His report satisfied this requirement.

Two days later, the Committee publicly released the report. Impeachment proceedings against Clinton were initiated soon thereafter. It was the third impeachment process started into a US President. The first was Andrew Johnson in 1868 and the second was Richard Nixon in 1974.

The Starr report

Starr's report and the impeachment proceedings triggered a fierce debate. A majority of the American public believed that the Congressional Republicans, driven by partisan motivations to obstruct the Clinton presidency, used the Starr report to move forward with a case that was not worthy of impeachment.

Others believed that Starr and Congress had no choice but to proceed as they did given the weight of the evidence that President Clinton lied under oath and endeavored to obstruct the investigation. By the end of the saga, both parties let the 1978 law that created the Office of the Independent Counsel expire.

Without an Independent Counsel statute, the Justice Department had to develop an alternative mechanism for appointing an independent prosecutor. On July 9, 1999, regulations were published in the Code of Federal Regulations to fill the void. The regulations provided a mechanism for the Attorney General to appoint a Special Counsel to investigate and, when appropriate, to prosecute matters when the Attorney General concluded that extraordinary circumstances existed and that the public interest would be served by removing most of the responsibility for investigating a matter from the ordinary channels within the Justice Department.

A principal concern of the drafters of the new Special Counsel regulations was the need to ensure that future Independent Counsel would not be empowered to draft and release to the public a comprehensive final report. (Note: Michael Zeldin, a co-author to this piece, was an Independent Counsel, who, like Starr, filed a multi-hundred page report detailing his investigative findings.)

New limits

In place of the Independent Counsel Act mandating a final public report, sections 600.8 and 600.9 of Title 28 of the Code of Federal Regulations greatly constrained the way that the special prosecutor could present his/her findings to the Justice Department, to Congress and, importantly, to the American public.

As reflected in the discussion notes to the regulations , the drafters were concerned with two principal issues pertaining to the final public report:

First, it was believed that the need to file a final public report created an incentive for Independent Counsel to over-investigate their case to avoid potential public criticism for not leaving any stone unturned.

Second, the public reporting requirement created potential harm to individual privacy interests, in part, because, while federal prosecutors commonly do not make public their decisions not to pursue a case, the Independent Counsel Act legally mandated the Independent Counsel to make their determinations public.

To address these concerns, the regulations imposed a limited final reporting requirement on all future Special Counsel. Instead of a full public report, the Special Counsel only is authorized to submit a confidential final report to the Attorney General. This confidential report is to be handled by the Justice Department in the same way as any internal documents are to be treated in a federal criminal investigation. (Meaning that the no-comment, no disclosure rules would apply.)

Recognizing that a strict no-comment rule would not be acceptable politically in high profile investigations, a limited accommodation was made. To ensure that the interests of the public in being informed of, and understanding the reasons for, the actions of the Special Counsel were addressed, the regulations obligate the Attorney General to notify Congress upon the receipt of the Special Counsel's final report and to "provide an outline of the actions and the reasons for them."

Nothing in the Special Counsel regulations directly authorizes the final report to be released publicly or transmitted to Congress.

This means that if Mueller and Barr were to follow strictly the limited reporting obligations established in the current Special Counsel regulations (Barr testified he would do just this during his confirmation hearings), the American public would remain in the dark. Moreover, because Congress has not played an active, public oversight role in the investigation until very recently the American public has not had another outlet for evaluating the key issues of concern.

What would be next?

So, where does this lead us if the Mueller "confidential report" and/or Barr's "brief notification" to Congress fail to provide the full-throated clarity America has been waiting for patiently?

The obvious answer is robust Congressional oversight. If the final report and the underlying material gathered by Mueller are not turned over to the oversight committees (as would have been the case under the Independent Counsel Act), Congress will be under great pressure to expand its investigations to replicate the Mueller investigation and to release publicly its findings.

Richard Nixon famously said that the American people deserve to know if their president is a crook. While there is no corroborated evidence that President Donald Trump has violated any law, the American people deserve to see the full Mueller report. They deserve to know if there was any "collusion" between the Trump campaign and the Russian government and if President Trump endeavored to obstruct the investigation in violation of law or in ways that would amount to grounds for impeachment. And, they need to understand fully the underlying reasons for Mueller's conclusions and decisions.

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Beyond the immediate investigation, this entire process has brought to light the need to reform how future investigations are handled. Congress needs to find a solution that forges a middle ground between what was believed to be a problem with the Independent Counsel Act and what has surfaced as a problem with the current Special Counsel regulations. Unless they do, the public will be left without answers to important questions that they have a right to know, and that would be bad for our democracy.