(Reuters) - Special Counsel Robert Mueller is preparing to submit to U.S. Attorney General William Barr a report detailing his findings in the investigation into Russia’s role in the 2016 presidential election and any links to the Trump campaign.

FILE PHOTO: Robert Mueller, as FBI director, testifies before the U.S. Senate Judiciary Committee on Capitol Hill in Washington. Sept. 16, 2009. REUTERS/Yuri Gripas/File Photo

Mueller has been looking since May 2017 into whether U.S. President Donald Trump’s campaign conspired with Russia and whether Trump unlawfully sought to obstruct the probe. Mueller already has indicted or secured guilty pleas from 34 people, including six associates of Trump, as well as three Russian entities.

Here is a look at possible scenarios following the completion of Mueller’s report.

REPORT FINDS TRUMP INVOLVED IN RUSSIA CONSPIRACY

Among those who already have pleaded guilty or have been convicted are: former Trump campaign chairman Paul Manafort; former Trump personal lawyer Michael Cohen; former national security advisor Michael Flynn; and former Trump campaign aides Richard Gates and George Papadopoulos. Others indicted include Trump adviser Roger Stone and Russian intelligence officers.

But the central question is whether Mueller will find that Trump himself played a role in a conspiracy with Moscow to boost his chances of winning the election or committed obstruction of justice to try to impede the Russia probe. Trump has denied collusion and obstruction.

If Mueller’s report reveals a willingness by Trump to collude with Russia or contains evidence of direct coordination involving the Republican president, such findings could be the starting gun for the Democratic-led House of Representatives to launch the impeachment process set out in the U.S. Constitution to remove a president from office.

Current Justice Department policy opposes bringing criminal charges against a sitting president.

Stone’s indictment points to instances in which people connected to the campaign communicated with him about Wikileaks, the website that released emails that U.S. officials have said Russians stole from Democrats to harm Trump’s Democratic opponent Hillary Clinton. For example, after a July 2016 release of emails stolen from the Democratic National Committee a “senior Trump campaign official was directed to contact STONE about any additional releases” by Wikileaks, the indictment stated. The sentence’s wording left open the possibility that Trump himself directed the campaign official.

Sam Nunberg, a former Trump aide and Republican political consultant, said any evidence that Trump was willing to work with Moscow, even without proof that he actually did that, might be enough for Democrats to draw up articles of impeachment.

“That’s impeachable for the Democrats,” Nunberg said.

The U.S. Constitution sets specific grounds for impeachment: treason, bribery or “other high crimes and misdemeanors.” If the House approves any articles of impeachment, the Senate then would hold a trial to determine whether to remove the president from office. The Senate is controlled by Trump’s fellow Republicans. Only two presidents have been impeached in American history, and neither was removed.

There is also the issue of obstruction. Legal experts have pointed to Trump’s firing of former FBI director James Comey while he was leading the Russia probe, Comey’s allegation that Trump asked him to end the investigation of Flynn, and the president’s dangling a possible pardon to Manafort among other acts that may amount to obstruction of justice.

Barr, months before Trump named him as attorney general, last year wrote an unsolicited memo to the Justice Department arguing Mueller should not be permitted to investigate obstruction by the president.

NOBODY IN TRUMP CAMPAIGN IMPLICATED IN RUSSIA CONSPIRACY

Mueller’s cases against Manafort and Stone have come the closest to showing coordination between Trump’s campaign and Russia. Manafort shared election polling data with his Russian associate Konstantin Kilimnik, who prosecutors have said is tied to Russian intelligence. Manafort attended a June 2016 meeting at Trump Tower in New York with other campaign officials with a Russian lawyer who promised “dirt” on Clinton. Mueller also found that Stone communicated with Wikileaks and the Russian hacker dubbed Guccifer 2.0.

But Mueller’s evidence made public to date falls short of demonstrating Trump and his campaign colluded with Russia. Collusion is a non-legal term often used to describe acts that in a criminal context in this investigation likely would translate to a charge of conspiracy against the United States.

If Mueller’s report goes no further, it could set back any Democratic effort to impeach Trump. But House Democrats could proceed with their own investigations that could cause Trump ongoing political damage heading into his 2020 re-election bid.

“If nothing more comes out than what is public then I think Trump could claim victory,” said Nelson Cunningham, a former federal prosecutor in New York and White House lawyer under Democratic President Bill Clinton.

REPORT IMPLICATES OTHERS IN CONSPIRACY BUT NOT TRUMP

Transcripts of closed court hearings this month indicated Mueller considers Manafort’s alleged lies about his interactions with Kilimnik to be “at the heart” of the probe into possible collusion between Trump’s campaign and Russia.

But that disclosure suggested Mueller was still trying to determine whether collusion occurred. In addition to sharing polling data, court filings show, Manafort and Kilimnik discussed a “Ukrainian peace plan,” a reference to Kremlin-friendly proposals to resolve the Ukraine conflict and end U.S. sanctions on Russia.

It is possible Mueller’s report will show that Manafort or others in Trump’s orbit conspired with Russians but there was no credible evidence Trump himself was involved or aware. While politically damaging to Trump, such a finding may not be enough to trigger an impeachment effort, though it could fuel House committee investigations.

“It’s not enough to show the Russians used their people,” said Robert Ray, who served as the second independent counsel in the 1990s Whitewater probe involving the Clintons’ business dealings, adding there would need to be proof that Trump’s people actively colluded to the point that it violated the law.

“I don’t think it occurred,” Ray said.