Comey, who was sacked while leading the probe into Russia's interference in the election, said Trump asked him to drop an investigation into former national security adviser Michael Flynn and implied Trump may have become the subject of investigation himself for interfering in the FBI's work.
Fired FBI Director James Comey's Senate Intelligence Committee testimony this week that he felt "queasy" amid an assertion former Attorney General Loretta Lynch was providing cover for Hillary Clinton last summer is enough to prompt a Senate Judiciary Committee investigation, Sen.
Democratic senators repeatedly criticized Sessions for dispatching Rosenstein to testify Tuesday in his place about the Justice Department's budget to an Appropriations subcommittee.
The leaders of the Senate Intelligence committee said in a statement issued Wednesday that they "look forward to future engagements" with Robert Mueller.
Lawmakers for weeks have demanded answers from Sessions, particularly about meetings he had last summer and fall with the Russian ambassador to the United States, Sergey Kislyak.
On Jan. 27 and February 14, Feinstein noted, citing recent testimony by fired FBI Director James Comey, Trump met with Comey privately to first ask for his loyalty and then to ask him to drop the federal probe into Flynn. "Nice", Trump wrote in his first tweet. He said at his January confirmation hearing that he had not met with Russians during the campaign.
The Washington Post reported late Wednesday that Mr Mueller was seeking interviews with three Trump administration officials who weren't involved in Mr Trump's campaign: Dan Coats, the director of national intelligence; Michael Rogers, the head of the National Security Agency; and Richard Ledgett, the former NSA deputy director.
A close Trump associate said this week the president was considering firing Mueller, although the White House later denied it.
Ranking Member Dianne Feinstein (D-CA) "says that she wants the Judiciary Committee to investigate potential obstruction of justice", CNN's Manu Raju told committee Chair Chuck Grassley (R-IA) in the Senate's hallways.
"We're going to leave that to a conversation with Feinstein", Grassley responded.
He, however, said that whatever Trump did was "a very disturbing thing, very concerning".
The former Federal Bureau of Investigation director also testified that the agency had believed Sessions was "inevitably going to recuse" for reasons he could not elaborate on.
"We need the judiciary committee to step up and carry its weight", Sen. In congressional testimony last week, Comey said he gave a copy of that memo to Richman - whom he identified only by his job - so he could provide details to a reporter. Donald Trump didn't request that meeting as president-elect, Jim Comey did.