Rod J. Rosenstein, nominee to be deputy attorney general, testifies before the Senate Judiciary Committee. (Aaron P. Bernstein/Reuters)

THOUGH PRESIDENT TRUMP’S opening weeks have been chaotic and dispiriting, the nation’s new chief executive has still managed to make a few good choices. One of his best was nominating Rod J. Rosenstein to be the No. 2 at the Justice Department. The sooner the Senate confirms him, the sooner the administration will have another adult in its top ranks. So it’s unfortunate that Mr. Rosenstein faced demands from Democrats at his Tuesday confirmation hearing that no one in his position should accede to.

As deputy attorney general, Mr. Rosenstein would oversee the daily operations of a vast, 115,000-person bureaucracy responsible for enforcing laws on everything from hate crimes to antitrust. After nearly three decades in the Justice Department, serving under presidents of both parties, “Rod Rosenstein has demonstrated throughout his long career the highest standards of professionalism,” Sen. Benjamin L. Cardin (D-Md.) testified before the Senate Judiciary Committee. The senator praised Mr. Rosenstein’s “nonpartisan” approach and noted his wide support among Democratic officials in Maryland, where Mr. Rosenstein serves as U.S. attorney and has had notable success prosecuting gang crime and political corruption.

Instead of that record, Mr. Rosenstein’s hearing was dominated by the recusal of Attorney General Jeff Sessions last week from issues involving Russia and the 2016 presidential election. With Mr. Sessions sidelined, Justice Department decisions regarding any investigation into Russia’s meddling and contacts between Mr. Trump’s circle and Russian officials would fall to Mr. Rosenstein. He assured senators that “political affiliation is irrelevant to my work” and promised to “support any properly predicated investigation related to interference by the Russians or by anybody else in American elections.”

But that was not enough for Sen. Richard Blumenthal (D-Conn.), who told Mr. Rosenstein that “I will oppose your nomination if you are unwilling to commit to appoint a special prosecutor.” Mr. Rosenstein offered a model reply: “I view it as an issue of principle that as a nominee for deputy attorney general I should not be promising to take action on a particular case,” he said. “And I believe that if I were to do that in this case, some future deputy attorney general nominee would be here. And he’d be asked to make a similar commitment. And they’d say, ‘Well, Rosenstein did it, why won’t you?’ ”

If, as was the case with Mr. Sessions, Mr. Rosenstein had been a top official in the Trump campaign, it would have been appropriate for him to prospectively recuse himself, as Mr. Sessions did on all matters relating to Hillary Clinton. But as it is, Mr. Rosenstein would not enter the Justice Department’s top ranks with such a clear appearance of a conflict of interest. It is entirely appropriate for Mr. Rosenstein to do what any good prosecutor would — refuse to prejudge a law enforcement question before reviewing the full record, including information that is not publicly available.

We believe that Russian interference in the election is a matter of such grave public importance that appointing a special counsel would add to the Justice Department’s appearance of independence and integrity. But we respect Mr. Rosenstein for refusing to pre-commit. So should the Senate.