Yet in several moments, Mr. Sessions seemed committed to revealing as little as possible, particularly about his interactions with the president. Pressed on his rationale for keeping quiet, Mr. Sessions allowed that Mr. Trump had not invoked executive privilege concerning the testimony of his attorney general.
“I am protecting the right of the president to assert it if he chooses,” Mr. Sessions said.
Democrats accused Mr. Sessions of trying to have it both ways: observing that only Mr. Trump can assert executive privilege but sidestepping questions on the grounds that he might, eventually.
In previous administrations, cabinet-level officials have at times declined to answer questions from lawmakers by arguing that their communications might be subject to executive privilege in the future, even if the president had not yet invoked that power.
The Justice Department pointed to memos from the administration of Ronald Reagan to bolster Mr. Sessions’s case, saying that his reasoning was consistent with “longstanding executive-branch-wide practice.”
But experts consider the matter a constitutional gray area — and little precedent exists for such a witness strategy amid sprawling investigations into a foreign power’s interference in the American democratic process.
“We are talking about an attack on our democratic institutions, and stonewalling of any kind is unacceptable,” Senator Ron Wyden, Democrat of Oregon, said at one point.
“I am not stonewalling,” Mr. Sessions shot back. “I am following the historic policies of the Department of Justice.”
Still, Mr. Sessions’s appearance did little to move the White House beyond the shadow of Russia-tinged investigations, which have for months consumed the president and his team — often with firestorms of Mr. Trump’s own making.
On Tuesday, as the attorney general came to Capitol Hill, the administration was straining to play down suggestions that Mr. Trump is considering firing Robert S. Mueller III, the special counsel investigating possible ties between the president’s associates and Russian officials.
Mr. Sessions spoke from the same hearing room where James B. Comey, the former F.B.I. director, testified last week that Mr. Trump had tried to derail an investigation into Michael T. Flynn, the president’s former national security adviser. Mr. Comey, whom Mr. Trump fired last month, also accused the president of lying and defaming him and the F.B.I.
That testimony colored much of Tuesday’s hearing, with Democrats pressing Mr. Sessions on several key elements of Mr. Comey’s account. Among the questions: Why was Mr. Sessions involved in Mr. Comey’s firing — months after Mr. Sessions had removed himself from involvement in the investigations after failing to disclose past contacts with the Russian ambassador?
“It is absurd, frankly,” Mr. Sessions began, “to suggest that a recusal from a single specific investigation would render the attorney general unable to manage the leadership of the various Department of Justice law enforcement components that conduct thousands of investigations.”
Mr. Sessions also addressed Mr. Comey’s recollection of a private meeting in February with Mr. Trump, when Mr. Comey said the president pressured him to drop the Flynn investigation. Mr. Trump asked that the two be left alone, the former director has said, and Mr. Sessions left the room after initially staying behind. Mr. Comey said he later told Mr. Sessions to never again leave him alone with Mr. Trump.
On Tuesday, Mr. Sessions seemed to confirm at least fragments of Mr. Comey’s rendering.
“I do recall being one of the last ones to leave,” he said. “I don’t know how that occurred.”
But Mr. Sessions said he did not see the arrangement as “a major problem,” calling Mr. Comey an experienced official who “could handle himself well.”
After the Oval Office encounter, Mr. Sessions recalled, Mr. Comey “expressed concern to me about that private conversation.”
“And I agreed with him, essentially, that there are rules on private conversations with the president,” Mr. Sessions continued, disputing Mr. Comey’s account that he had said nothing in reply. “But there’s not a prohibition.”
Justice Department policy calls for only the attorney general or the deputy attorney general to brief the president on law enforcement investigations, in part to limit the possibility of political interference. Should those officials designate a subordinate to update the president, department policy stipulates the attorney general or his deputy be told what was discussed.
Mr. Sessions, generally well-liked by fellow senators before leaving Congress, had already created a credibility deficit with some former colleagues in his new role. During his confirmation hearings this year, he told lawmakers that he had no contacts with Russian officials during the campaign.
But in March, Mr. Sessions was forced to acknowledge meeting Ambassador Kislyak on two occasions. On Tuesday, Mr. Sessions attributed the confusion in part to “a rambling question” at the time from Senator Al Franken, Democrat of Minnesota.
The unverified reports of the possible third meeting at the Mayflower Hotel are said to be traced to raw intelligence from American spy agencies that lawmakers have reviewed. But American officials have said it is not corroborated.
Any confirmation of such a meeting could prove devastating for Mr. Sessions, whose relationship with Mr. Trump has already showed signs of strain. Mr. Trump has vented privately about Mr. Sessions’s decision to recuse himself from any Russia-related investigations conducted by the Justice Department, suggesting the move was unnecessary.
At one point in recent weeks, Mr. Sessions offered to resign, telling Mr. Trump he needed the freedom to do his job. Senators did not ask him about that on Tuesday.
But Mr. Sessions did demonstrate sweeping support for the president’s agenda, at times bouncing in his chair as he spoke during his opening statement. He said that questions about his conduct had “only strengthened my resolve to fulfill my duty.”
Often, Mr. Sessions found refuge in the questioning of Republicans on the committee, who accused Democrats of overreaching.
Senator Tom Cotton, Republican of Arkansas, suggested that his counterparts had ventured into the realm of spy fiction, citing the rumored meeting at the Mayflower.
“Have you ever, in any of these fantastical situations,” he began, “heard of a plotline so ridiculous that a sitting United States senator and an ambassador of a foreign government colluded at an open setting, with hundreds of other people, to pull off the greatest caper in the history of espionage?”
Mr. Sessions smiled slightly.
“Thank you for saying that,” he said. “It’s just like, through the looking glass. I mean, what is this?”