Many a career in the Trump administration has imploded after a scathing missive from the president’s Twitter account. But for Attorney General William Barr, it was a congratulatory tweet from Donald J. Trump’s handle — not a critical one — that has thrown his office into disarray this week.

“Congratulations to Attorney General Bill Barr for taking charge of a case that was totally out of control and perhaps should not have even been brought,” the President wrote on Wednesday, the day after the Justice Department overrode the recommendations of its own lawyers and lowered the amount of prison time it would seek for Trump ally Roger Stone.

The four DOJ lawyers who prosecuted the case against Stone, a Trump confidante who was convicted of charges including witness tampering and lying to investigators in a case stemming from special counsel Robert Mueller’s investigation, had recommended an original sentence of up to nine years. Trump tweeted that their recommendation was “horrible and very unfair,” and within hours, DOJ leadership intervened and said they instead recommended three to four years, prompting the four lawyers to quit.

The latest scandal to hit the Justice Department, amplified and exacerbated by Trump’s running commentary on social media, has renewed long-running questions about Barr’s independence from the President and the degree to which Trump’s views can influence decisions at DOJ.

Although the Justice Department is nested within the executive branch, presidents and attorneys general have traditionally taken great pains to make sure there is no appearance of improper political influence over prosecutorial decisions. As President, Trump has often tested those limits, perhaps most visibly in openly pressuring and berating his previous attorney general Jeff Sessions over his recusal from the special counsel’s Russia investigation. When Barr was confirmed to the post in February 2019 to replace Sessions, many Democrats hoped he would be a strong institutionalist who would resist Trump’s encroachment into DOJ business.

But over the course of his first year on the job, Barr has instead emerged as a staunch defender of the President, making a series of decisions that have protected Trump at key moments in his presidency and eroded the appearance of political independence at the department.

Barr spoke out about the controversy on Thursday, telling ABC News that he will not “be bullied or influenced by anybody” and that the President’s tweets “make it impossible for me to do my job.”

“I’m going to do what I think is right,” Barr said. “I cannot do my job here at the department with a constant background commentary that undercuts me.”

Now Barr is being asked to testify to Congress about his actions. The House Judiciary Committee announced on Wednesday that Barr will appear the following month, writing in a letter to the Attorney General that his “pattern of conduct in legal matters relating to the President… raises significant concerns,” including in the Stone sentencing.

Justice Department spokeswoman Kerri Kupec told the Daily Beast on Tuesday that the decision to override the sentencing recommendations was made Monday night, before Trump’s tweet. She said DOJ had not consulted with the White House about the decision, and Barr was unaware of Trump’s views before the department made its decision. She did not respond to request for comment on Wednesday.

Whether or not Trump ever spoke directly to the department, Barr “should be insulating these prosecutors from the president,” says Peter Zeidenberg, a former federal prosecutor at the Justice Department. “He should be saying… notwithstanding the president’s personal feelings, these cases are all being handled in a professional manner, not based on the whims of the president.”

“It really tarnishes the reputation of the department,” Zeidenberg says.

Top Democrats including House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer have already called for investigations into the ordeal. And while Republicans have largely stayed quiet or defended the Justice Department processes, high-ranking Democratic officials from the past have also weighed in with dismay. “Do not underestimate the danger of this situation: the political appointees in the DOJ are involving themselves in an inappropriate way in cases involving political allies of the President,” Eric Holder, former attorney general under President Obama, tweeted. “This affects the rule of law and respect for it. Unprecedented.”

The House Judiciary Committee also asked Barr to testify about “the creation of a new ‘process'” in the Department of Justice, by which Trump’s personal attorney Rudy Giuliani “can feed the Department of Justice information, through you, about the President’s political rivals.”

On Monday, Barr had acknowledged there was an “intake process” to evaluate information gathered by Giuliani from Ukrainian sources about former Vice President Joe Biden and his family, a matter that was central to the impeachment inquiry into Trump. But, Barr said, the Justice Department has an “obligation to have an open door to anybody who wishes to provide us information that they think is relevant.”

Not everyone agrees. House Judiciary Chairman Jerrold Nadler, a Democrat from New York and one of the House’s impeachment managers in the Senate trial that ended last week, wrote a letter to Barr expressing “serious concern” about the process and writing, “Any official relationship between Mr. Giuliani and the Department raises serious questions about conflicts of interest—both for the Department, generally, and for you, specifically.”

Previously, Barr has also said that he believes the FBI investigation into possible coordination between the Trump campaign and Russia was based “on the thinnest of suspicions that… were insufficient to justify the steps taken,” and that he believes “spying” occurred on Trump’s campaign. When Mueller submitted his final report to Barr last year, Barr determined Trump had not obstructed justice, though Mueller had explicitly declined to reach that conclusion. In a press conference in April 2019 about the report’s conclusion, Barr went further than the language in the report, echoing Trump’s own phrase in saying multiple times that there was “no collusion” between the Trump campaign and Russia.

The meddling in the Stone sentencing is just the latest scandal to chip away at the Department of Justice’s painstakingly cultivated reputation for being apolitical, says Zeidenberg. “It’s just so easy to destroy it. You can have a thousand cases that are handled appropriately, and then you have this type of a fiasco, and you destroy all that work.”

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Write to Tessa Berenson at tessa.berenson@time.com.