Sen. Jeff Sessions (R-AL) is sworn in during his attorney general confirmation hearing on Jan. 10 in Washington. (Matt McClain/The Washington Post)

ON TUESDAY the Senate Judiciary Committee will consider President Trump’s nominee for attorney general, Sen. Jeff Sessions (R-Ala.). As with any potential Justice Department leader, a primary question is whether Mr. Sessions will defend the separation between White House political interests and Justice Department decision-making, which should recognize no interest beyond fairly enforcing the law.

At a hearing this month, Mr. Sessions bolstered his promise to maintain the Justice Department’s credibility by pledging to recuse himself from decisions relating to Hillary Clinton’s email server or the Clinton Foundation. This was welcome: The statements Mr. Sessions made during the campaign about these matters would have cast doubt on his impartiality.

Yet Mr. Sessions declined to make a similar commitment on another, potentially graver issue: questions surrounding any Russian influence on last year’s election and the new administration.

The New York Times and the Wall Street Journal have reported that a federal counterintelligence task force has been examining possible links between the Russian government and various players in Mr. Trump’s orbit. These include national security adviser Michael Flynn, who now sits at the center of U.S. foreign policy, and whose communications with Russian officials, first reported by The Post’s David Ignatius, have been scrutinized. The White House says that these communications consisted of holiday greetings, logistical discussions about arranging phone calls between Russian President Vladimir Putin and Mr. Trump, and other innocuous matters. If that is so, Mr. Flynn has nothing to fear from a federal probe, which, given the high concern in many quarters, should continue as long as any questions linger.

When Judiciary Committee Democrats pressed Mr. Sessions on how he would handle election hacking prosecutions or investigations of potential connections between Trump associates and Russian authorities, Mr. Sessions repeatedly responded: “I am not aware of a basis to recuse myself from such matters. If a specific matter arose where I believed my impartiality might reasonably be questioned, I would consult with department ethics officials regarding the most appropriate way to proceed.”

But the basis for recusal is clear. Like Mr. Flynn, Mr. Sessions played a key role in the president’s campaign. At the least, Mr. Sessions would raise the appearance of a conflict if he made law enforcement decisions related to that campaign. He should commit to recusing himself now.

Mr. Trump has tapped Rod J. Rosenstein, a respected career prosecutor, to be deputy attorney general. Mr. Sessions should have no qualms about entrusting him with these politically vexing issues. It would raise confidence in his Justice Department and save him plenty of headaches. The Senate should insist on such a commitment before it votes.