The decision to reduce the prison sentence faced by the self-described “dirty trickster” led to four DOJ prosecutors resigning from the case – amid fears the department was being unduly influenced by the Oval Office to offer preferential treatment for Mr Trump’s close confidant.

Now in an open letter 1,142 former employees of the government department have called the attorney general’s decision to intervene on a case following anger from the president the behaviour of an autocracy.

The growing list of signatories, a group of Democrat and Republican appointees which includes Bush-administration deputy attorney general Donald Ayer, said the move constituted “a grave threat to the fair administration of justice”.

“In this nation, we are all equal before the law”, the letter said. “A person should not be given special treatment in a criminal prosecution because they are a close political ally of the president.

Everyone Trump has fired or forced out Show all 13 1 /13 Everyone Trump has fired or forced out Everyone Trump has fired or forced out John Bolton Trump claimed to have fired Bolton, his national security adviser, while Bolton claimed he offered to resign. An anonymous White House source that Bolton's departure came as a result of the national security adviser working too independently of the president AFP/Getty Everyone Trump has fired or forced out Anthony Scaramucci Scaramucci lasted only six days in his role as Trump's communications director before being fired by John Kelly, the incoming chief of staff Getty Everyone Trump has fired or forced out Rick Perry Rick Perry announced his resignation just as he became embroiled in the president's impeachment scandal. The White House said Mr Perry was asked by Donald Trump to work with Rudy GIuliani in regards to Ukraine. AP Everyone Trump has fired or forced out Rex Tillerson Tillerson, Trump's first secretary of state, was fired after a series of clashes with the president over policy Getty Everyone Trump has fired or forced out James Mattis Mattis served as secretary of defense from the beginning of Trump's administration until retiring on 1 January 2019. However, the president later claimed that he had "essentially fired" Mattis Getty Everyone Trump has fired or forced out James Comey Comey was fired as director of the FBI early in Trump's presidency after serving in the role for four years prior. His dismissal is widely thought to have been related to the Russia investigation Getty Everyone Trump has fired or forced out Reince Priebus Priebus, Trump's first chief of staff, was forced out after six tumultuous months AFP/Getty Everyone Trump has fired or forced out David Shulkin Veterans affairs secretary Shulkin claims that he was fired, the White House claims that he resigned Getty Everyone Trump has fired or forced out John Kelly Kelly, Trump's second chief of staff, was forced out after 17 months in office. His departure was a confused affair though it is clear that Trump wanted Kelly out AFP/Getty Everyone Trump has fired or forced out Michael Flynn Flynn lasted 24 days as Trump's national security adviser before being fired for lying to the FBI Getty Everyone Trump has fired or forced out Lee Cisna Cisna served as director of citizen and immigration services between October 2017 and June 2019 before being asked to resign amid a major personnel change in the department of homeland security Everyone Trump has fired or forced out Madeline Westerhout Westerhout served as Trump's personal assistant after leaking private information about his family AFP/Getty Everyone Trump has fired or forced out Mira Ricardel Ricardel was forced out of her role as Deputy National Security Advisor after first lady Melania Trump publicly called for her to be fired

“Governments that use the enormous power of law enforcement to punish their enemies and reward their allies are not constitutional republics; they are autocracies.”

Stone, who was found guilty in November on a number of counts including obstructing a congressional investigation into Russian interference in the 2016 presidential election, had been set to face a prison sentence of nine years following recommendations from justice department prosecutors.

But senior officials in the department, including Mr Barr, overruled the sentence to replace it with a more lenient alternative after the president wrote on Twitter that almost a decade of prison time for the 67-year-old was “a horrible and very unfair situation”.

Both the attorney general and the president have since attempted to distance themselves from claims of political interference, with Mr Trump saying he has “so far chosen not to” exert influence over criminal proceedings handled by the department.

Shortly after four of his own prosecutors removed themselves from the case, Mr Barr appeared to chide his commander in chief while stating he was “not going to be bullied or influenced by anybody … whether it’s congress, a newspaper editorial board, or the president”.

However critics point out that the more lenient sentencing approved of by the president still stands. The letter added: “Mr Barr’s actions in doing the President’s personal bidding unfortunately speak louder than his words.

“Those actions, and the damage they have done to the Department of Justice’s reputation for integrity and the rule of law, require Mr Barr to resign.”