Jeffrey Rosen is President Trump’s nominee to be the next deputy attorney general. (Andrew Harrer/Bloomberg News)

Jeffrey A. Rosen, President Trump’s nominee to take over the Justice Department’s No. 2 position, sought Wednesday to assuage lawmakers’ concerns about his lack of criminal law experience but shied from making firm commitments on how he would handle special counsel Robert S. Mueller III’s final report and the ongoing investigations the work spawned.

Rosen, the deputy secretary of transportation, has not worked in the Justice Department, and much of the questioning at his confirmation hearing before the Senate Judiciary Committee focused on whether he is up to the task of managing its day-to-day operations.

In the morning’s tensest exchange, Sen. Richard Blumenthal (D-Conn.) asked Rosen whether he would promise the full release of Mueller’s report. Rosen noted he would be answering to Attorney General William P. Barr, who has committed only to releasing a redacted version of the document.

“If I’m confirmed, I would be the deputy attorney general, and I would be working with the attorney general,” Rosen said.

His voice low, Blumenthal noted that he voted against Rod J. Rosenstein, the current deputy attorney general, when Rosenstein would not promise in advance to appoint a special counsel to investigate whether the Trump campaign had conspired with Russia.

“I will vote against you if you fail to commit that you will respect the institutional authority and obligation of the United States Congress to review that report,” Blumenthal said. “Will you support complete and total disclosure?”

Rosen would not offer a definitive promise. Because Republicans control the Senate, he could be confirmed without Democratic support.

If confirmed, Rosen would almost certainly become involved in managing how the Justice Department handles requests from Congress for more information on Mueller’s work. Although the Justice Department is expected to release a redacted version of Mueller’s final report within a week, that is unlikely to completely satisfy lawmakers or short-circuit the ongoing political and legal spats over the document and its underlying materials.

Throughout the hearing, Rosen noted repeatedly that he was not yet in the department and could only comment on what he had observed publicly. He said, for example, that he could not endorse or dispute Barr’s assertion Wednesday that “spying” on a political campaign occurred in the course of intelligence agencies’ investigations into Russian interference in the 2016 election.

“I just don’t have the facts,” he said, adding later that “if it happened, it would be troubling.”

Rosen promised broadly to act in accordance with department policies.

“I am going to do the right thing in accordance with the law and the rules, and the ethical requirements at every juncture,” he told Blumenthal, adding later that he was willing to rebuff inappropriate requests from the White House.

“If the appropriate answer is to say no to somebody, then I will say no,” Rosen said.

He suggested, in response to a question from Sen. Amy Klobuchar (D-Minn.), that he would let any cases that Mueller’s work had generated continue as normal.

“If I’m confirmed, I would expect in all criminal investigations and prosecutorial matters that they proceed on the facts and the law,” Rosen said.

Several lawmakers noted that Rosen’s lack of criminal experience concerned them.

Sen. Dianne Feinstein (Calif.), the committee’s highest-ranking Democrat, said in her opening remarks that the position Rosen is seeking is important — overseeing the department’s law enforcement and national security functions — and that it was even more vital “in light of President Trump’s repeated calls to investigate his political rivals.” She contrasted Rosen with Rosenstein, whom she noted came to the job with decades of experience as a federal prosecutor and had a deep understanding of the Justice Department’s norms.

“My big concern is that because Mr. Rosen has never before served as a prosecutor, he may not have that same intimate knowledge of those practices and those precedents,” Feinstein said.

Rosen said he would “not be the first person” with a background like his to serve as deputy attorney general, and he would install in his office people with prosecutorial experience.

“I take very seriously the fact that there are aspects of criminal law and criminal procedure that are somewhat different and have very important ramifications,” Rosen said.

As happens with many Trump nominees, lawmakers pressed Rosen on the president’s controversial policies and positions — including migrant family separations and the decision not to defend the Affordable Care Act. Klobuchar asked about how he would handle Justice Department policies concerning the treatment of reporters — an area of particular concern in an administration that is critical of the news media.

Rosen notably seemed to suggest that he would not seek to jail journalists for doing their jobs — a commitment that Eric Holder, President Barack Obama’s attorney general, had made — though with the caveat that they could not break the law.

“I would agree with you in this sense, that I don’t think journalists should be punished for doing their jobs. I think like all citizens, if they break the law . . . they’re subject to the same rules as everybody else,” Rosen said. “I agree with you that people should not be punished for simply being reporters.”