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The special counsel Robert Mueller is said to be preparing a report of his findings in his investigation into whether President Donald Trump attempted to obstruct justice.

Mueller could be putting together the report because he doesn't think he has the authority to indict Trump based on Department of Justice policies.

But legal experts cautioned that a blistering report of Mueller's findings could be as dangerous to Trump's presidency as an indictment.

The most important revelation in a Washington Post report out Tuesday night is not that the special counsel Robert Mueller told President Donald Trump's lawyers he isn't a criminal target of the Russia investigation.

Rather, it's that Mueller is preparing a report about Trump's actions in office and potential obstruction of justice.

Mueller is tasked with investigating Russia's interference in the 2016 US election, and a significant thread in the inquiry is whether the president sought to obstruct justice when he fired James Comey as FBI director last year.

Comey had publicly confirmed the existence of the Russia investigation months before his firing, and he was in charge of overseeing it at the time of his dismissal.

Since then, news reports and a string of public statements from Trump have raised questions about the circumstances surrounding Comey's firing and whether Trump had the right to fire the FBI director if his intent were to hamper a criminal investigation involving him and his associates.

News that Mueller is now preparing a report about those circumstances lays out some important clues about the direction the investigation may be heading in.

It could indicate one of three things, according to Jeffrey Cramer, a former federal prosecutor who spent 12 years at the Department of Justice:

The president did nothing wrong and will not be charged. Mueller found some indication of criminal activity but might not have enough evidence to indict Trump. Mueller does have enough evidence to indict Trump but may decide he does not have the authority to charge the president based on Department of Justice precedent.

The policy in question centers on a September 1973 memo, written during Richard Nixon's presidency, by the DOJ's Office of Legal Counsel. Robert Dixon, then the office's head, wrote at the time that a sitting president could not be indicted because doing so may hinder the executive branch from "accomplishing its constitutional functions" in a way that cannot "be justified by an overriding need."

Nixon's solicitor general, Robert Bork, also submitted a court brief in October 1973 arguing that sitting presidents are immune to indictments and criminal proceedings. In 2000, the head of the Office of Legal Counsel under President Bill Clinton reaffirmed Bork's and Dixon's judgments.

But The New York Times unearthed another legal memo last year arguing that a sitting president could be indicted. It was written in 1998 by the office of the special prosecutor Kenneth Starr, who spearheaded the Whitewater investigation that eventually led to Clinton's impeachment in the House of Representatives.

Starr tapped Ronald Rotunda, a professor of constitutional law and ethics, to write the memo, which significantly narrowed the premise that a president is immune to indictments. Rotunda wrote that the Constitution granted "limited immunity" to lawmakers in some contexts, but not to the president.

A blistering report from Mueller could be as dangerous to Trump as an indictment

Trump's status as a subject of the investigation and not a target could change once he interviews with Mueller. AP Photo/Pablo Martinez Monsivais

Legal experts said that while Rotunda's memo was compelling, it remained unlikely that Mueller would indict Trump.

They added that the ball would ultimately be in Congress' court — where a report from Mueller could prove most consequential.

Mueller's office has so far charged 19 people with crimes, including 13 Russian nationals. The indictments against those individuals, as well as the charges against the former Trump campaign chairman Paul Manafort, draw a stark and detailed picture of the defendants' alleged criminal conduct.

"Similar to the Manafort and Russian indictments, I expect any report [about Trump] to lay out in painstaking detail the facts they uncovered," Cramer said.

Mueller is mandated to provide reports of his findings to Rod Rosenstein, the deputy attorney general who appointed him as the special counsel in May. But whether those findings are released to the public is Rosenstein's decision.

Alex Whiting, a former federal prosecutor who is now a professor at Harvard Law School, said he found it "striking" that "Mueller seems to be preparing the report with an expectation that it will eventually become public."

He added: "Once the investigation is completed, I think it will be very difficult to keep Mueller's conclusions secret."

Several of Trump's advisers are afraid Mueller could issue a blistering report about the president's actions, The Post said. The report, in turn, could bolster some lawmakers' argument that Trump should be removed from office.

"The president's personal risk is primarily on the impeachment front," Keith Whittington, a professor of politics at Princeton University who's an expert on impeachment, told The Post. "Even if there are not things that lead to indictment, there may be matters that warrant an impeachment investigation and proceedings."

Experts also cautioned that Mueller had not obtained the most critical component of the obstruction-of-justice investigation: a face-to-face interview with the president.

Trump has reportedly been "champing at the bit" to sit down with the special counsel — against the advice of his lawyers, some of whom believe their client could land himself in legal jeopardy if he makes a misleading statement during the interview.

Like Whittington, Cramer said Trump could face ramifications beyond an indictment if he were to stray off script while speaking with Mueller.

"Trump's version of the facts — which even a biased observer would have to admit aren't always accurate — could provide some fodder for the report to Congress and any action they deem appropriate," Cramer said.

Trump's a 'subject' — not a 'target' — of Mueller's probe

Legal experts also said the fact that Mueller had not secured an interview with Trump could be a significant part of why investigators see the president as a subject and not a target of the investigation.

A subject is someone under criminal investigation, which Trump has been since Mueller started building the obstruction case against him last year.

A target, meanwhile, is someone who prosecutors have enough evidence to charge with a crime.

"Prosecutors often withhold a final determination on who is designated a 'target' until all the evidence is in and evaluated," Whiting said.

Trump is most likely the last person Mueller's team needs to interview before drawing its conclusions in the obstruction case.

If Trump refuses to submit to an interview, Mueller could respond by serving the president with a grand-jury subpoena. The courts could then decide whether a sitting president can be compelled to appear before a grand jury.

"The one thing that will not happen is for the president to refuse the interview and Mueller simply shrugging his shoulders and walking away," Cramer said. "There is nothing in Bob Mueller's impressive past ... to indicate he will balk at that fight. No one in their right mind would want Bob Mueller on their trail."