(CNN) Jeffrey Rosen, set to take over as acting attorney general next week, is an unknown quantity in Trump White House politics, even after serving for more than a year as No. 2 to Attorney General William Barr, the especially vocal and controversial public face of the Justice Department.
With Barr's December 23 departure nearing, Rosen will lead the Justice Department for President Donald Trump's final month in office, putting the former corporate lawyer in the middle of what may be a political dust storm created by a lame-duck President who still refuses to concede and has made clear he wants his opponents prosecuted or even jailed.
"I am honored at the trust and confidence that President Trump has placed in me to serve as Acting Attorney General upon the departure of Attorney General Bill Barr," Rosen said in a statement Tuesday evening.
"I will continue to focus on the implementation of the Department's key priorities, including protecting national security, promoting public safety by combatting violent crime and drugs, safeguarding civil rights and liberties, and maintaining the rule of law," he continued, calling it "a privilege" to lead the department.
A deputy attorney general always takes a backseat to the department's top appointee, but Rosen's public profile has been even lower than is typical. He's largely stayed out of Barr's most controversial moments in the spotlight, such as when the attorney general overrode career prosecutors in the criminal prosecutions of Trump associates Michael Flynn and Roger Stone.
But Rosen has stepped up in major corporate litigation, including playing a central role opposite opioid makers and the tech community.
In the coming weeks, he could also be managing incoming messages from the White House and Trump's Twitter feed related to pardons of the President's friends and even family, and about politically charged investigations, including those that could help Trump continue to spread falsehoods about the election.
According to one Justice Department official who knows him, Rosen does not relish making the types of decisions that would put him in the center of political storms. And it's not yet known if he'll fall in line with Trump or push back on behalf of a department where political appointees are quietly leaving and career staff are preparing for the next administration.
"He's not the type who likes to make decisions," the official said. "Barr is all fire and fury. Rosen does things for the right reasons."
"Rosen is quiet, but strong," another source familiar with him told CNN.
Barr's early departure puts Rosen, who had also served in Trump's Transportation Department as deputy secretary and as a general counsel at agencies during the George W. Bush administration, in the unusual position of leading the department as an acting official for one final month of a presidency.
He could potentially stay in the job until President-elect Joe Biden's attorney general pick is confirmed, as has happened in prior administration turnovers at the request of the incoming administrations.
Previous Senate-confirmed Attorneys General Loretta Lynch and Michael Mukasey stayed on until the last days in office of Presidents Barack Obama and George W. Bush, respectively, before handing the department over to their deputy AGs -- those in Rosen's position now -- until the next administration's nominee could be confirmed, for instance.
Rosen's deliberative approach stems from his decades in private practice handling complex litigation for companies. At Justice, Barr treated Rosen more like his counsel, with the attorney general staying involved in the most attention-getting moments for the department instead of stepping aside for Rosen to manage solely, according to a Justice Department official.
"Barr has held the stage the entire time. So we don't know how much of a role Rosen had in so many of the key decisions," said Julie Rodin Zebrak, a Democratic political consultant who previously spent two decades at the Justice Department and worked as a deputy chief to a former deputy attorney general. "We don't really know a ton about him."
Rosen remains somewhat of a mystery to even the attorneys who have worked out of the main Justice building, according to current and former department officials who spoke to CNN.
Internal Justice Department documents, released by the department in recent months under the Freedom of Information Act, give little indication of how involved Rosen has been behind the scenes on controversial matters. For instance, he was kept apprised of the fallout in the department related to the sentencing of Stone but it's not clear how involved he was in Barr's choice to override the prosecutors on the case.
Rosen's lack of prosecutorial experience was an issue when he first took on the role of deputy, but he did take the lead on major actions by the Justice Department, including the antitrust lawsuit against Google and the criminal plea deal with OxyContin maker Purdue Pharma.
The effort to craft a case against Google, which is ongoing, centered on Rosen's office, according to two former Justice Department officials. When the lawsuit was announced in October, Rosen told reporters that "nothing is off the table" when it came to the consequences Google could face.
During his Senate confirmation to the deputy attorney general position, Rosen pledged to push back against any improper influence he might face. Rosen was asked by a senator in writing how he would respond if the President asked him to do anything that was illegal. Rosen first noted that he thought "this hypothetical scenario is unlikely to occur," then wrote, "If I were nonetheless directed to do something illegal, I would resign rather than carry out an illegal order."
At his Senate confirmation hearing in April 2019, he said, "If the appropriate answer is to say no to somebody, then I will say no."
Rosen may face political pressures similar to the kinds placed on Barr and Trump's first attorney general, Jeff Sessions, as the President continues to publicly press for leniency for his supporters who are charged with crimes, for investigations into voter fraud that could spread doubt about the reality of the election and for consequences for investigators who tracked Russian interference in the 2016 US election.
Barr's departure comes on the heels of an interview with The Associated Press that angered Trump, where Barr declared that the Justice Department had found no evidence of widespread voter fraud, and of reports that the attorney general had kept the investigation of Hunter Biden quiet until after the election.
The issue of voter fraud again appeared in Barr's resignation letter on Monday, with the attorney general saying he had updated Trump that day on a Justice Department review of voter fraud "and how these allegations will continue to be pursued." The department hasn't provided more details on what that review may entail, and state and federal judges have repeatedly rejected as evidence-less Trump's assertions that widespread voter fraud existed this year.
The President may also push the Justice Department on the investigation of Hunter Biden -- the President-elect's second son -- and for results from now-special counsel John Durham, who was handpicked by Barr to investigate the FBI's handling of the early Russia investigation and has been used by Republicans to cast doubt on findings about the Trump campaign's receptiveness to Russian interference in 2016.
Republicans on Capitol Hill have already called for a special counsel on Hunter Biden. The appointment of one would position the criminal probe with a prosecutor specially brought in to lead an investigation, putting it a half-step away and protected in some aspects from the next president's administration.
Already, federal prosecutors in Delaware are working with the IRS and FBI investigators to issue subpoenas and obtain interviews related to Hunter Biden on tax-related issues and his business dealings with China, CNN has reported.
"There's going to be all of this pressure" on Rosen in the final days, a Justice Department official said.
This story has been updated to include Rosen's statement on serving as acting attorney general.