The scandal embroiling the White House and US justice department in the case of Donald Trump’s former confidant Roger Stone deepened on Thursday as senior Democrats condemned an “abuse of power” by the president and called for the chief justice of the supreme court to intervene to protect the judge in the case.

And a senior law enforcement official quit after her oversight of the prosecution of Stone cost her a top job at the treasury, CNN reported on Thursday.

The abrupt resignation of Jessie Liu, who previously led the US attorney’s office in Washington, poured fresh fuel on a political fire lit by the president’s perceived interference at the justice department.

While Trump continued to deny wrongdoing, Democrats urged the chief justice, John Roberts, to defend the independence of the judicial branch from the president’s continued attacks.

Liu had overseen numerous cases stemming from the special counsel Robert Mueller’s Russia investigation as well as that of the former FBI deputy director Andrew McCabe, who has long been assailed by Trump.

She reportedly resigned from the treasury department on Wednesday evening after her nomination as its under-secretary for terrorism and financial crimes, a Senate-confirmed position, was unceremoniously pulled by Trump in what appeared to be retaliation.

Critics warned that it fitted a pattern. The president had previously criticised the career prosecutors who recommended a prison sentence of seven to nine years for his longtime friend and adviser Stone, describing it as “horrible” and a “miscarriage of justice”.

Just hours later, the justice department called for a more lenient sentence, prompting all four prosecutors to resign in protest. Trump has also tweeted criticism of the US district court judge Amy Berman Jackson, who is scheduled to sentence Stone on 20 February, and thanked William Barr, the attorney general, for “taking charge” of the case. But he still wasn’t done.

On Thursday, Trump turned his wrath on the jury that convicted 67-year-old Stone in November on seven counts of lying to Congress, obstruction and witness tampering. Citing a Fox News report that accused some of the jurors in the case of political bias, he tweeted: “This is not looking good for the ‘Justice’ Department.”

He received backing from the chair of Senate judiciary committee. Lindsey Graham of South Carolina, a Trump loyalist, posted: “If media reports are accurate – about juror bias in the Roger Stone case – I hope the court will take such allegations seriously.”

Barr, meanwhile, aired his views in an interview with ABC News, saying that Trump’s tweets about Stone case “make it impossible for me to do my job’”.

“I think it’s time to stop the tweeting about Department of Justice criminal cases,” Barr told ABC on Thursday.

The attorney general emphasized Trump “has never asked me to do anything in a criminal case”, but he acknowledged the president’s comments undercut his authority.



The White House press secretary, Stephanie Grisham, later said Trump “wasn’t bothered” by the comments.

Nancy Pelosi and Chuck Schumer condemned the president’s behaviour. Photograph: Alex Brandon/AP

Democrats have denounced Trump’s conduct as an “assault on the rule of law”. Chuck Schumer, the minority leader in the Senate, reiterated his demand for an investigation by the justice department’s inspector general and called for the chief justice to intervene, noting that he had previously defended a judge attacked by Trump.

“Well, President Trump is once again attacking a federal judge – in this case Judge Amy Berman Jackson, who is presiding over the Stone case,” Schumer said in a speech on the Senate floor. “The nation now looks again to Chief Justice Roberts to make clear to President Trump that these attacks are unacceptable.”

Schumer added: “Now would be the time for Chief Justice Roberts to speak up. Now would be the time for the chief justice to directly and specifically defend the independence of this federal judge. I hope he will see fit to do that, and to do it today.”

Roberts presided with an even hand over the Senate impeachment trial, which ended last week with Trump’s acquittal. Democrats warn that verdict taught Trump only one lesson: that he can get away with anything.

Senator Chris Murphy of Connecticut tweeted: “Convince me that what Trump has done since the impeachment vote isn’t worse than what he did to warrant impeachment. Like we warned, acquittal has turned out to be a green light for him to take a wrecking ball to democracy.”

Meanwhile, all 10 Democrats on the Senate judiciary committee wrote to Graham asking that the committee start investigation into political interference at the justice department.

“The justice department’s mission ‘to ensure fair and impartial justice for all Americans’ requires that its prosecutorial decisions remain free from political influence. It’s becoming clear that this is not happening,” the senators wrote. “That’s why the judiciary committee should investigate involvement of political appointees in this and other cases and hear directly from Attorney General Barr.”

Democrats did make one breakthrough in their oversight efforts. They say Barr has agreed to appear before the House judiciary committee at the end of next month. He is certain to be questioned over what pressure, if any, Trump exerted on behalf of his friend.

The House speaker, Nancy Pelosi, told reporters that Barr “deeply damaged the rule of law”. She added: “The attorney general has stooped to such levels. What a sad disappointment to our country.”

She said: “This is an abuse of power – that the president is again trying to manipulate federal law enforcement to serve his political interest. This is not what America is about. It is so wrong.”

Trump has declined to comment on whether he will eventually grant Stone a pardon. “I don’t want to say that yet,” he told reporters on Wednesday.