Mueller replied: “Yes.” Buck continued: “You believe that he committed – you could charge the President of the United States with obstruction of justice after he left office?” Again, the response was “Yes.”

The Special Counsel’s report into whether Donald Trump was the Muscovian candidate for the White House concluded that Trump may have committed obstruction of justice on at least 10 occasions. But Mueller had decided that a 1973 Justice Department decision that a sitting president cannot be indicted meant that charging Trump with federal crime would be “unconstitutional”.

The 43-year-old ruling on presidential privilege has also protected Trump, to varying extents, from a number of investigations and lawsuits, including a year-long battle over his tax returns.

But with his impending departure from the White House, he is now quite vulnerable. He has lost the safety of office and the service of his loyal Attorney General, William Barr. Some prosecutors had become worried about taking on not only the former president but his friends. After the prison sentence of Trump’s friend Roger Stone was cut by Barr, they expressed private concern to the media that the Attorney General would not back them. That constraint has now gone.

Trump is the subject of 15 inquiries, criminal and civil, by nine federal, state and district agencies into his business and personal finances, including his tax affairs, his campaign, his inaugural committee, and charities associated with him.

Many of these are on track to go ahead separately. But because of the egregious nature and scale of Trump’s alleged offences, there have been calls for a special commission to examine the evidence. Eric Swalwell, a Democrat Congressman from California, said: “When we escape this Trump hell, America needs a Presidential Crime Commission. It should be made up of independent prosecutors who look at those who enabled a corrupt president; example one, sabotaging the mail to win an election.”

Ken Starr, the independent prosecutor who investigated Bill Clinton over the Monica Lewinsky scandal, commented during the Mueller investigation that the Special Counsel would either recommend impeachment or that Trump would face indictment once he was out of office.

Starr was subsequently part of Trump’s defence team on Congressional impeachment hearings over his alleged attempts to pressure Ukrainian President Volodymyr Zelensky into opening an investigation into the business activities of Joe Biden’s son Hunter. Trump was found guilty in the House of Representatives and won in the Republican-controlled Senate.

Whether a Democrat administration would pursue Trump on the Mueller report remains to be seen. Biden himself has remained cautious on the issue. But Kamala Harris has held that the Justice Department would have “no choice” but to act. The vice-president elect said while running for the Democratic nomination: “I do believe we should believe Bob Mueller when he tells us, essentially, that the only reason an indictment was not returned is because of a memo in the Department of Justice that suggests you cannot indict a sitting president. But I’ve seen prosecution cases based on much lesser evidence.”

During the 2016 campaign, the Trump team, led by his national security advisor Michael Flynn – who was subsequently convicted in the Mueller investigation – had routinely egged on chants of “lock her up” about “crooked Hilary”.

No charges were ever brought against Hilary Clinton, but the administration has launched investigations into former FBI director James Comey and his deputy Andrew McCabe. Trump had also threatened to sack Barr if he did not indict Barack Obama, Joe Biden and many others for the supposed scandal he called “Obamagate” – relating to a vague theory that Obama officials framed Trump over the investigation into collusion with Russia – and declared that prosecutions will follow once he was re-elected.

There have been reports that Trump may pardon himself before leaving office. It remains unclear whether he can do so constitutionally and the issue came up during the confirmation hearing for Amy Coney Barrett to the Supreme Court.

But even if he could carry out the unprecedented act by a president of pardoning himself, he would still be susceptible to the state and local charges he is facing. One, by the US Attorney’s Office for the Southern District of New York, cited Trump (“individual 1”) in the charges laid against his former personal lawyer Michael Cohen over campaign finance crimes related to hush-money paid to women, one of them Stormy Daniels, who allegedly had affairs with Trump.

Cohen, who pleaded guilty to the charges, had claimed under oath that Trump had directed him to make the illegal payments and that he was reimbursed for the payments by the Trump Organisation. The former lawyer, now bitterly estranged from Trump, has predicted his former boss “may soon be the first president to go from the White House straight to prison”.

In another case, Cyrus Vance Jr, the district attorney for Manhattan, is investigating what his office has described as “possibly extensive and protracted criminal conduct at the Trump Organisation”. As well as Trump’s taxes, it will examine whether Trump and his company engaged in bank fraud, insurance fraud, criminal tax fraud and falsification of business records.

Trump and his legal team have challenged a subpoena asking his accounting firm for eight years of tax returns and financial records. Five courts have dismissed the challenge. Trump also lost an appeal to the Supreme Court seeking immunity from state grand jury subpoena.

The New York Attorney General is also conducting an investigation into whether the Trump organisation manipulated the value of assets to secure loans and tax benefits. Among the lines of inquiry are tax breaks at the Trump Seven Springs complex in New York and the Trump National Golf Club in Los Angeles. There are also probes into the valuation of a Trump office tower in Wall Street and writing off of a $100m loan on the Trump International Hotel and Tower in Chicago.

The prosecutors say it is a civil investigation and not being conducted in coordination with any law enforcement agencies at present. But, they say, it could become a criminal matter if evidence emerges to support that. Lawyers for the Trump Organisation have claimed that New York Attorney General Leititia James is politically motivated and had tried to postpone a deposition by one of the president’s sons until after the election. This was rejected by the court and Eric Trump recently made his deposition remotely.

Trump also faces legal action by alleged victims of his sexual assaults, such as the magazine writer E Jean Carroll, who claimed that Trump raped her in a Manhattan department store in the 90s. They are suing him for defamation after he accused them of making up the attacks. On these cases, too, Trump had sought to benefit from his position. Last month, in an extraordinary move, Attorney General Barr substituted the Justice Department as the defendant in place of Trump in the Carroll case.

The Department’s lawyers claimed that Trump should not be sued because he had made his remarks about Carroll in the “course of an official White House response to press inquiries”, even though what he said was about a matter which took place decades before he was elected.

Carroll’s lawyers accused Barr’s decision of distorting the search for justice. “There is not a single person in the United States – not the president and not anyone else – whose job description includes slandering women they sexually assaulted,” they said in a statement.

It appears unlikely that the Justice Department, under Biden, would continue to take over Trump’s role. There may well be a desire to draw a line after the extraordinary turbulence and divisions of the Trump years. In his speech as president-elect, Biden spoke of a “time to heal”, pledging “not to divide, but to unite the country”.

Jack Goldsmith, professor at Harvard Law School, said to the broadcaster NPR: “Whether that’s good for the country is a very hard question that’s going to be very messy. Whether it’s good for the Biden administration [...] to be absorbed in being the first administration to ever prosecute a prior president – those are very hard questions.” But Goldsmith also acknowledged that, “it’s not at all clear that looking forward and not looking back is an available option”.

Such has been the toxic nature of politics with Donald Trump, the aggression the former president had shown towards his opponents, the sheer volume of allegations against him, that it will be very difficult to halt the calls for legal reckonings.