Sessions is expected to face sharp questioning from his former Senate colleagues about his role in the investigation into contacts between Trump campaign associates and Russia during the 2016 election.
The Justice Department said today that Sessions requested tomorrow's committee hearing be open because he "believes it is important for the American people to hear the truth directly from him."
His testimony follows fired FBI Director James Comey's riveting session before the same Senate panel last week. Comey spoke of receiving pressure from President Donald Trump to drop a probe into former National Security Adviser Michael Flynn's contacts with Russia.
Trump's aides have dodged questions about whether conversations relevant to the Russia investigation have been recorded, and so has the president.
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Republicans have pressed Trump to say whether he has tapes of private conversations with Comey and provide them to Congress if he does -- or possibly face a subpoena.
"I don't understand why the president just doesn't clear this matter up once and for all," said Sen. Susan Collins, R- Maine, a member of the intelligence committee, referring to the existence of any recordings. She described Comey's testimony as "candid" and "thorough" and said she would support a subpoena of any tapes if needed.
Lankford said Sessions' testimony tomorrow will help flesh out the truth of Comey's allegations, including Sessions' presence at the White House in February when Trump asked to speak to Comey alone.
Comey alleges that Trump then privately asked him to drop a probe into former national security adviser Michael Flynn's contacts with Russia.
Comey also has said Sessions did not respond when he complained he didn't "want to get time alone with the president again."
Senator Jack Reed, DRI, said "there's a real question of the propriety" of Sessions' involvement in Comey's dismissal, because Sessions had stepped aside from the federal investigation into contacts between Russia and the Trump campaign. Comey was leading that probe.
Reed said he also wants to know if Sessions had more meetings with Russian officials as a Trump campaign adviser than have been disclosed.
Democratic Senator Dianne Feinstein of California, a member of the Intelligence committee, sent a letter to Senator Chuck Grassley, R-Iowa, urging him to investigate possible obstruction of justice by Trump in Grassley's position as chairman of the Judiciary Committee. Feinstein is the top Democrat on that panel and a member of both.
Feinstein said she was especially concerned after National Intelligence Director Dan Coats and National Security Agency Director Michael Rogers refused to answer questions from the intelligence committee about possible undue influence by Trump.
Sessions stepped aside in March from the federal investigation into contacts between Russia and the campaign after acknowledging that he had met twice last year with the Russian ambassador to the US.
The former senator from Alabama told lawmakers at his January confirmation hearing that he had not met with Russians during the campaign.
As for the timing of Sessions' recusal, Comey said the FBI expected the attorney general to take himself out of the matters under investigation weeks before he actually did.
Comey declined to elaborate in an open setting.
Collins and Feinstein spoke yesterday on CNN's "State of the Union and Lankford appeared on CBS' "Face the Nation." Reed was on "Fox News Sunday.