House Speaker Nancy Pelosi (D-Calif.) took aim Thursday at Attorney General William P. Barr, accusing him of having “deeply damaged the rule of law” by withdrawing the Justice Department’s sentencing recommendation for President Trump’s longtime friend and associate, Roger Stone.

“What a sad disappointment to our country,” Pelosi said of Barr, who Trump nominated to lead the Justice Department in late 2018. “The American people deserve better.”

She called on Republicans in the Senate to speak out and launch a probe into the matter.

“This all must be investigated,” she said. “The American people must have confidence in our nation’s system of impartial justice.”

A jury convicted Stone in November on charges of witness tampering and lying to Congress about his efforts to gather damaging information about Trump’s 2016 presidential election opponent Hillary Clinton.

On Tuesday, Trump criticized as unduly harsh the initial sentencing recommendation of seven to nine years made by front-line prosecutors. Shortly thereafter, the Justice Department signaled that it would seek a more lenient sentence for Stone, a move that prompted all four career prosecutors to withdraw from the case and one to resign from the government.

Trump congratulated Barr for “taking charge” of the matter and has since begun targeting U.S. District Judge Amy Berman Jackson, who will determine Stone’s fate when he appears in her courtroom next week.

Pelosi’s criticism of Barr comes one day after the House Judiciary Committee announced that the attorney general is expected to testify March 31 regarding his handling of the Stone case and other recent incidents that it said “raise grave questions” about his leadership.

In a floor speech earlier Thursday, Senate Minority Leader Charles E. Schumer (D-N.Y.) called for Supreme Court Chief Justice John G. Roberts Jr. to defend Jackson against Trump’s efforts to delegitimize her.

Roberts, Schumer noted, had previously issued a rare rebuke of Trump’s criticism of an “Obama judge” who ruled against the administration.

“We do not have Obama judges or Trump judges, Bush judges or Clinton judges,” Roberts had said in his November 2018 statement. “What we have is an extraordinary group of dedicated judges doing their level best to do equal right to those appearing before them.”

Schumer said Thursday that “now would be the time for Chief Justice Roberts to speak up” in defense of Jackson.

“Now would be the time for the chief justice to directly and specifically defend the independence of this federal judge,” he said. “I hope he will see fit to do that and to do it today.”

Schumer and the nine other Democrats on the Senate Judiciary Committee also wrote a letter to the panel’s chairman, Sen. Lindsey O. Graham (R-S.C.) on Thursday asking him to immediately launch an investigation into alleged political interference at the Department of Justice in the wake of the Stone news.

“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 10 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.”

At her news conference, Pelosi directly criticized Trump, arguing that he “thinks he’s above the law.”

“This is an abuse of power that the president is again trying to manipulate federal law enforcement to serve his political interests,” she said.

She described the decision by the four prosecutors to withdraw from the Stone case as “an act of courage” and said that Republicans must not be silent on the matter.

“Where are the Republicans to speak out on this blatant violation of the rule of law?” Pelosi asked. “AG Barr has deeply damaged the rule of law by withdrawing the DOJ’s sentencing recommendation.”

A Justice Department spokeswoman did not immediately respond to a request for comment.

Later Thursday, in an interview with ABC News, Barr pushed back against Trump’s criticism of the Justice Department, saying that he is “not going to be bullied or influenced by anybody.”

Certain presidential statements and tweets, Barr said, “make it impossible for me to do my job.”

One judge who did weigh in Thursday was Chief U.S. District Judge Beryl A. Howell of Washington. In a statement, Howell responded to Trump’s attacks on Jackson and defended the integrity of the courts.

“The Judges of this Court base their sentencing decisions on careful consideration of the actual record in the case before them; the applicable sentencing guidelines and statutory factors; the submissions of the parties, the Probation Office and victims; and their own judgment and experience,” Howell said. “Public criticism or pressure is not a factor.”

Senate Majority Leader Mitch McConnell (R-Ky.), meanwhile, pointed the finger at Democrats in a floor speech Thursday morning in which he accused them of violating the country’s “norms and traditions” by voting to impeach Trump.

“It was they who included political bloodlust at the expense of our institutions,” he said. “There has been much discussion about the foreign adversaries who seek to reduce the American people’s faith in our democracy and cause chaos and division in our country. Rightly so, but we must also demand that our own political leaders exercise some self-restraint and not do the work of our adversaries for them.”

Democrats have repeatedly accused McConnell of violating norms by blocking President Barack Obama’s 2016 Supreme Court nominee, Judge Merrick Garland, until after that year’s presidential election, ultimately costing Garland a spot on the court.

Robert Barnes, Spencer S. Hsu, Ann E. Marimow and Matt Zapotosky contributed to this report.