On Saturday, the president described his attorney general as a “big disappointment” on Twitter after it emerged that the Department of Justice had begun an investigation into Hunter Biden’s taxes as early as 2018 - but did not make existence of the enquiry public until after the election.

CNN reported that Mr Trump was considering firing Mr Barr over the issue.

According to a Wall Street Journal report, Mr Barr was aware of a federal investigation into the president-elect’s son’s tax and business records for a year but worked to keep it quiet during the election.

Mr Trump appeared angered that Mr Barr did not politicise the investigations. He asked on Saturday why the attorney general did not “reveal the truth to the public, before the Election, about Hunter Biden”.

But Mr Barr told a source that he was not “intimidated” by the president’s attacks, CNN reported.

"Barr cannot be intimidated by Trump. This is the real story. None of this matters - it's the deposed king ranting. Irrelevant to the course of justice and to Trump's election loss," the source said on Saturday.

The source described the relationship between Mr Trump and Mr Barr as “a Cold War”.

Mr Barr has said that the presidential election was not rigged, despite repeated false claims by Mr Trump and his campaign, amid failed attempts to overturn president-elect Biden’s victory.

The electoral college will certify the election results on Monday.