As he readies to end his term in office, a suggestion has emerged - that Donald Trump could pardon himself or his family.
Media reports, quoting unnamed sources, say Mr Trump has suggested to aides he is considering granting a pardon to himself in the final hours of his presidency, coming alongside further recent presidential pardons.
Mr Trump has tweeted in the past that "all agree the US President has the complete power to pardon".
To some experts, this would be like a judge presiding over their own trial. Others though say Mr Trump may be correct - although that is not to say it would be a good idea.
How do presidential pardons work?
The right of US presidents to issue pardons is enshrined in the constitution.
Under Article II, Section 2, Clause 1, presidents have "power to grant reprieves and pardons for offenses against the United States, except in cases of impeachment".
In practice a president could offer clemency or a commutation, i.e. reducing a prison sentence. A president can also offer a full pardon, in essence an official statement of forgiveness for a crime.
An individual does not have to be charged or convicted to receive a pardon, and a president cannot pardon people over state-level crimes.
In the context of the Russia investigation, Mr Trump could grant immunity to aides or family members, limiting Mr Mueller's scope.
So could Trump pardon himself?
The short answer is we do not know, given the short wording but broad application of the constitution, and the fact there is no precedent for a US leader issuing such a pardon.
Some legal experts say no, citing an opinion issued by the Justice Department days before Richard Nixon's resignation that he could not pardon himself "under the fundamental rule that no one may be a judge in his own case".
"The Justice Department was right that guidance could be found in the enduring principles that no one can be both the judge and the defendant in the same matter, and that no one is above the law," wrote Laurence H Tribe, Richard Painter and Norman Eisen in the Washington Post.
Others though say the constitution does not preclude a self-pardon.
"A self-pardon might well be outrageously improper... but the response the Constitution creates for such misconduct is impeachment, a political rather than criminal remedy," Mark Tushnet, a law professor at Harvard University told Vox.
Would it help him though?
While there are differing opinions among experts about whether Mr Trump could pardon himself, there is more consensus that such a move would be fraught with difficulties.
Jonathan Turley, a professor at George Washington University Law School, told the LA Times a president pardoning himself would raise serious questions "of an abuse of power".
It would also not apply to possible state charges, and only federal charges.
Two University of Chicago law professors, Daniel Hemel and Eric Posner, writing in the New York Times, argue that if Mr Trump pardoned relatives he could open himself to the risk of being charged with obstruction of justice.
If he were to pardon himself, questions would follow about whether it is valid, and it could ultimately end up in the Supreme Court.
Who has been pardoned before?
Gerald Ford pardoned his predecessor Richard Nixon over the Watergate scandal.
He argued it was essential for the nation to move on. It is a decision still debated today - some say it cost him the 1976 election, others that he made the difficult, but right, choice.
Presidents have made sweeping pardons to heal national wounds, such as when President Andrew Johnson pardoned Southerners after the Civil War.
Bill Clinton caused uproar when he pardoned scores of people on his last day in office, including a brother-in-law and Marc Rich, a fugitive who had been indicted for tax evasion and fraud.
Perhaps the most famous beneficiary of President Obama's clemency was Chelsea Manning, the US Army Private sentenced to 35 years in jail for leaking documents to Wikileaks.
Who has Trump pardoned?
Mr Trump has made some controversial pardons.
They include his former national security adviser Michael Flynn, who was ensnared by the Special Counsel inquiry into alleged Russian meddling in the 2016 election.
In December, he issued a series of pardons, including his former campaign manager Paul Manafort, ex-adviser Roger Stone and the father of his son-in-law.
Mr Trump also pardoned four security guards involved in a 2007 massacre in Iraq.
There were also less contentious pardons and commutations.
In 2018, he pardoned Jack Johnson, boxing's first black heavyweight champ, convicted in 1913 of taking his white girlfriend across state lines, and the same year granted clemency for Alice Johnson, a 63-year-old grandmother jailed in 1996 on a non-violent drug charge.