Eric Columbus served as senior counsel to the deputy attorney general in the Department of Justice and as special counsel to the general counsel in the Department of Homeland Security during the Obama administration.

For decades, scholars have debated the question of whether the Constitution allows a sitting president to be indicted and tried while in office — and whether it would be prudent to do so. Two decades ago, independent counsel Kenneth Starr confronted these questions while investigating President Bill Clinton and answered yes to the first, but no to the second.

We don’t know what special counsel Robert S. Mueller III thinks of these questions — in general, or with respect to his ongoing investigation of the relationship between members of President Trump’s inner circle and Russian interference in the 2016 presidential election — but it doesn’t matter. A change in law since 1999 has taken the decision out of his hands.

Mueller won’t indict Trump. But here’s what you need to know to understand what may happen instead.

Appointed by a special panel of judges to replace an earlier independent counsel who had been investigating Clinton’s involvement in an Arkansas land deal, Starr sought and received permission from that panel to investigate allegations that Clinton had suborned perjury or obstructed justice in an effort to conceal his affair with White House intern Monica Lewinsky. The title “independent counsel” effectively meant that for purposes of the Clinton investigation, Starr was the attorney general, with the ultimate power to decide whom to prosecute and on what basis.

In response to concerns that independent counsels — not just Starr — were too powerful, Congress let the independent counsel statute expire in 1999 (while allowing ongoing independent counsel investigations to run their course). In its place, the Department of Justice published regulations that enabled the appointment of a “special counsel” with significantly narrower authority. As special counsel in the Russia probe, Mueller functions more like a U.S. attorney — albeit one with a purview defined by topic rather than geography — than a U.S. attorney general. He may be “special,” but he’s not “independent.”

He is confined in two ways: First, Mueller must abide by all Justice Department “rules, regulations, procedures, practices and policies” — as distinct from Starr, who could deviate from such policies where they were “inconsistent with the purposes” of the independent counsel statute. Second, Starr had unreviewable discretion, while any investigative or prosecutorial decision Mueller makes may be reviewed and disapproved by the attorney general. Because Attorney General Jeff Sessions, a prominent figure in Trump’s presidential campaign, recused (in essence, disqualified) himself from oversight of matters related to the Russia investigation, Deputy Attorney General Rod J. Rosenstein has served as acting attorney general for Mueller’s purposes.

So how does this affect whether Trump gets indicted? In 1973, the Justice Department’s Office of Legal Counsel (OLC) — essentially the government’s lawyers’ lawyers — determined that the president is constitutionally immune from indictment and criminal prosecution while in office. With his broad authority, Starr felt unbound by that opinion and ordered up his own from a conservative legal scholar, who determined that Starr could, in fact, indict Clinton, though he ultimately chose not to. In October 2000, the OLC reaffirmed its earlier opinion that a sitting president cannot be indicted.

It’s rare for an attorney general to undertake an action that the OLC has concluded would be unconstitutional. Even in matters of far less importance, the OLC’s learned and expert analysis almost always carries the day with government officials, especially where it has published lengthy opinions on the matter that would be gleefully cited by a litigant (in this scenario, President Trump) challenging the action on constitutional grounds. Even if Mueller does conclude that Trump has committed a crime, and that it would be both constitutional and prudent to indict him, and even if Rosenstein agrees in all regards — all of which are big “ifs” — Rosenstein almost certainly wouldn’t allow such an indictment.

Starr, of course, did not wash his hands of the matter when he decided not to indict Clinton. Rather, he issued a 445-page report cataloging in exhaustive and sometimes explicit detail Clinton’s sexual relationship with Lewinsky, outlining how the facts could give rise to impeachment. This report was mandated by the independent counsel statute, which required Starr to advise Congress of “any substantial and credible information” that “may constitute grounds for an impeachment.” Starr’s report provided a road map, and Clinton was, indeed, impeached by the House of Representatives in December 1998, although he remained in office because the Senate acquitted him in February 1999.

But Mueller cannot do this, at least not directly. The special counsel regulations, unlike the independent counsel statute, neither mandate nor allow Mueller to transmit a report to Congress. Rather, at the end of his work, he must provide a “confidential report” to the attorney general — Rosenstein, in Sessions’s stead — explaining his “prosecution or declination decisions.”

[Yes, Trump can fire Mueller. But a normal president would know not to try it.]

The regulations don’t say what format that report must take or what happens next. If Mueller believes he has information that could warrant impeachment, he could weave it into a narrative like the Starr Report. But even if Rosenstein wanted to make the report public, he would be limited by Federal Rule of Criminal Procedure 6(e), which imposes strict limits on the disclosure of grand jury materials. This rule, which has the force of law, is intended to preserve the integrity of grand jury investigations and encourage witnesses to testify fully and frankly. Rosenstein could, if he chose, issue a redacted report that conveys the gist of Mueller’s findings.

Of course, given the president’s apparent displeasure with Rosenstein, it’s possible that by then Trump will have replaced the deputy attorney general with a more compliant successor who would not affirmatively disclose the report. Or Trump could achieve the same result by replacing Sessions with a new attorney general who isn’t recused from supervising Mueller.

Congress could likely subpoena the report in its entirety pursuant to recognized exceptions to grand jury secrecy, including a Nixon-era precedent in which courts upheld a grand jury’s decision to transmit evidence and a sealed report to the House Judiciary Committee. Indeed, Congress could procure not only Mueller’s report, but all investigative files that relate to the president. It could then make the material public if it so chose, as it did with the Starr report.

The catch? Only congressional committee chairmen can issue subpoenas. With both the House and Senate under GOP control, Republicans could simply decline to do so. The 2018 midterm elections, therefore — and the potential for one or both houses of Congress to change hands — may be crucial to determining whether and when Mueller’s Trump-related work sees the light of day.

Remember, Mueller is an investigator, not a politician. He does not have a dog in the impeachment fight. His likely goals are, and should be, to dig up facts and bring them to light as warranted. With that in mind, he may have a couple of other cards to play.

He might be able to name Trump as an unindicted co-conspirator, an unusual step that prosecutors sometimes deploy when, for various reasons, it is impossible or impracticable to indict a specific person who participated in a criminal conspiracy. Justice Department rules impose significant limits on this practice, however, and it is uncertain whether Rosenstein would allow Mueller to do so. (It’s even less likely to occur if Rosenstein is no longer the decider.)

Alternatively, Mueller could trigger a reporting requirement in the special counsel regulations under which the attorney general must inform “the Chairman and Ranking Minority Member of the Judiciary Committees of each House of Congress” — both parties, in other words — at the end of the special counsel’s investigation, of any instance in which the attorney general vetoed a proposed action. Simply by proposing to indict Trump, Mueller could ensure that Congress gets the word. But this would be of only limited scope: instead of an evidence dump, it need only be a “brief notification, with an outline of the actions and the reasons for them.”

What all these scenarios have in common is that Congress, not the courts, will be the ultimate arbiter of whether Trump faces any direct consequences from Mueller’s investigation. Depending on the state of play come November, voters across the nation may be the ones who determine whether Congress decides even to consider that question. Elections have consequences, and one consequence of the midterms may be whether the American public finds out what Mueller has learned about Trump.