With only weeks left for Joe Biden to exercise his presidential powers, supporters of Julian Assange, both in Australia and the United States, are ratcheting up appeals for a pardon for the WikiLeaks founder.

The US president can issue pardons at any time during their term.

It's an extraordinary power that accompanies the highest office in the land, and allows them to pardon anyone for any federal crime.

Presidents can be lobbied directly, and they also receive recommendations from a pardon attorney that operates out of the US Justice Department, which receives and reviews applications for clemency.

"Sometimes we see clemency decisions come out around Thanksgiving or Christmas, for example, but they could be, and are, issued at any time," said Jeffrey Crouch, an expert on the process and a professor at American University in Washington DC.

"Clemency has traditionally been granted either as an act of mercy or to serve the public welfare.

"Occasionally a president will stray from these acceptable reasons and instead grant clemency for his own personal reasons."

So far in his term, Mr Biden has used pardons to facilitate prisoner exchanges with other countries, and to address marijuana offences.

But as his time in public life draws to a close, speculation is mounting about who he might pardon in the coming weeks.

As well as Assange, his son Hunter Biden, and even his successor, president-elect Donald Trump, have been mentioned as possible recipients of his clemency.

Previous presidents have made notable pardons of their own

In his first term, Trump made plenty of headlines for pardoning political allies, like his former campaign manager Paul Manafort, his former national security advisor Michael Flynn, and his political advisors Roger Stone and Steve Bannon.

He commuted the two-year sentence served by Charles Kushner — the father of Trump's son-in-law Jared Kushner — for preparing false tax returns, witness retaliation and making false statements.

He also pardoned Alice Johnson, a woman given a life sentence over a first-time drug offence, after being personally lobbied by celebrity Kim Kardashian.

Barack Obama keenly embraced the power as well, issuing more than 1,700 commutations and more than 200 pardons in his eight years in office — many granted to people who had received mandatory sentences for drugs charges.

Perhaps the most divisive pardon in US history was in 1974, when the Republican president Gerald Ford granted a full and unconditional pardon to his predecessor, Richard Nixon.

Mr Nixon had not been convicted of a crime or even criminally charged, but had resigned in disgrace after the Watergate scandal, and the possibility of charges hung over him.

Mr Ford pardoned him for any crimes he might have committed against the United States, saying he felt the pardon was in the best interests of the country — effectively telling the nation it was time to move on.

Mr Ford's approval rating dropped dramatically and he was defeated by Democrat Jimmy Carter at the presidential election two years later.

"The Nixon pardon by president Gerald Ford on September 8, 1974 was highly controversial," said Professor Crouch.

"It's impossible to say how much the Nixon pardon cost Ford, but it certainly is viewed now as having had a negative impact."

Exercising the power can come with political cost, which is why some presidents have waited until their final weeks in office to grant more controversial pardons.

Bill Clinton came under fire for pardoning members of a Puerto Rican paramilitary organisation, as well as Marc Rich, a fugitive who made substantial donations to his wife Hillary Clinton's Senate campaign.

On his final day in office, he also pardoned his brother Roger, who was arrested in 1985 for cocaine possession and a drug-trafficking conviction.

George W Bush controversially commuted the sentence of "Scooter" Libby, the former chief of staff to his Vice-President Dick Cheney, who had been convicted of perjury and obstruction of justice.

But Professor Crouch pointed out that both did so with a bit of political cover.

"[They] did so while they were 'lame duck' presidents and free from punishment at the ballot box," he said.

Could Julian Assange be in the mix for Biden?

Assange's supporters say a pardon would be an opportunity for the US government to prove it does not pursue journalists or media outlets with criminal prosecution.

In 2010, WikiLeaks published hundreds of thousands of leaked documents and diplomatic cables about the Iraq and Afghanistan wars.

A 2019 indictment asserted that Assange's actions risked serious harm to the national security of the United States, to the benefit of its adversaries, and put named human sources at grave risk.

He spent years in confinement — seven holed up in London's Ecuadorian embassy claiming asylum, and then nearly five in a UK prison awaiting extradition.

But in a bid to gain his freedom, Assange agreed to plead guilty earlier this year to a single charge, admitting to conspiring with then-US Army intelligence analyst Chelsea Manning to publish military documents on the website he founded, WikiLeaks.

He is now living in Australia and cannot enter the US without permission.

On a recent trip to Washington DC, his brother Gabriel Shipton said President Biden could send a strong message as he winds up his term.

"It's a way that President Biden can send a signal to the press freedom community that it isn't right to charge journalists and indict journalists and convict journalists of espionage for publishing material in the public interest," he told the ABC.

Two US congressmen from both sides of the aisle — Democrat Jim McGovern and Republican Thomas Massie — have also written a letter to the president urging him to consider a pardon.

"As you know, the decision to prosecute Mr Assange under the Espionage Act set off alarms among Members of Congress and advocates for freedom of expression and freedom of the press," they wrote.

In their letter, Congressman McGovern and Congressman Massie said the terms of the plea agreement set a precedent that "greatly deepens" concern.

"We therefore urge you to consider issuing a pardon for Mr Assange," they wrote in the letter, sent at the start of the month but only made public this week.

"A pardon would remove the precedent set by the plea and send a clear message that the US government under your leadership will not target or investigate journalists and media outlets simply for doing their jobs."

Mr Shipton said the Australian Prime Minister Anthony Albanese should leverage his own close relationship with Joe Biden and mention the pardon application directly.

"I think there's still a feeling in the electorate that this is a wrong committed against an Australian, and this could be a way for the prime minister to use his influence [with] the Biden administration and President Biden to right that wrong," he said.

Assange's supporters visited Canberra this week to meet with federal parliamentarians and highlight their campaign to secure a full pardon.

The prime minister's office did not respond to questions about whether Mr Albanese either supports or would advocate for a pardon.

Could Biden pardon Hunter? Or Trump?

As President Biden works to solidify his legacy during his final weeks in the Oval Office, another major question looms about the future of his only surviving son, Hunter.

The 54-year-old has two convictions on the books and sentencings for both crimes are scheduled for mid-December.

In the first case, a jury in his home state of Delaware found Hunter guilty of lying on a gun purchase form by saying he was not illegally using or addicted to drugs.

In the second case, he pleaded guilty in California to nine charges in a federal tax case, including tax evasion and filing fraudulent returns.

Hunter Biden has been open about his descent into drug addiction and alcoholism at the time of both offences.

In mid-June, when he was still seeking a second presidential term, his father said he would not pardon his son.

"I am not going to do anything," he said when asked on the sidelines of a G7 summit.

Of course, at the time, the president had more at stake: it was before he had withdrawn from the race and left his Vice President Kamala Harris to run, ultimately unsuccessfully.

The White House has indicated that even though President Biden is weeks away from retirement, he still has no plans to pardon his son.

Now set to succeed him in office, Donald Trump was previously asked by a conservative podcast host, Hugh Hewitt, if he'd pardon Hunter.

"I wouldn't take it off the books," Trump enigmatically responded.

"See, unlike Joe Biden, despite what they've done to me, where they've gone after me so viciously … Hunter's a bad boy. There's no question about it. He's been a bad boy."

Marc Thiessen, from the conservative-aligned think tank American Enterprise Institute, recently used his column in the Washington Post newspaper to argue the president should issue a blanket pardon for Trump as a final act of statesmanship, to attempt to bring a divided nation together.

"Biden is in a strong position to do this," Mr Thiessen wrote in his column.

"He is 82 years old, entering the sunset of his presidency and public life. Because he is never running for office again, he can endure the blowback from the left wing of his party, rise to the moment and clean up this mess for both our parties and for the country."

With barely over seven weeks left in the White House, Mr Biden doesn't have long to make a decision about which pardons he will issue.

On January 20, he'll hand over pardoning power, along with the keys to the Oval Office, to Trump.

The incoming president has already flagged a desire to pardon people charged over the January 6 attack on the US Capitol in 2021.

On the campaign trail, Trump made much of criminal charges he himself faced, calling them political weaponisation and election interference.

The question of whether he could even pardon himself now seems less likely to be tested.

Prosecutors sought to wind up two federal cases against him this week, due to a longstanding precedent against criminally pursuing a sitting president.