WASHINGTON — Impeachment investigators are exploring whether President Trump lied in his written answers to Robert S. Mueller III during the Russia investigation, a lawyer for the House told a federal appeals court on Monday, raising the prospect of bringing an additional basis for a Senate trial over whether to remove Mr. Trump.
The statement — during a hearing in a case over the House’s request for secret grand-jury evidence gathered by Mr. Mueller — came shortly after Mr. Trump said he may provide written answers about the Ukraine affair to impeachment investigators.
“Even though I did nothing wrong, and don’t like giving credibility to this No Due Process Hoax, I like the idea & will, in order to get Congress focused again, strongly consider it!” Mr. Trump wrote on Twitter, after insulting Speaker Nancy Pelosi.
But the hearing heightened focus on House suspicions that Mr. Trump had lied to Mr. Mueller’s investigators when he provide lawyerly, written answers to some questions. Mr. Trump had refused to testify orally to the special counsel’s office about what he knew and did during the 2016 campaign in relation to Russia’s election interference operation, or his later efforts to impede the inquiry.
In his responses, which were appended to the Mueller report, Mr. Trump denied that he was aware of any communications between his campaign and WikiLeaks. House lawyers had suggested in a Sept. 30 filing that some of the materials they were seeking bore on whether Mr. Trump was honest about that.
On Monday, Douglas Letter, the general counsel for the House told a federal appeals court panel that impeachment investigators have an “immense” need to swiftly see the grand jury evidence — redacted portions of the Mueller report, as well as the underlying testimony transcripts they came from.
“Was the president not truthful in his responses to the Mueller investigation?” Mr. Letter said, adding: “I believe the special counsel said the president had been untruthful in some of his answers.”
He was referring to Mr. Mueller’s congressional testimony in July. Near the end of the hearing, a lawmaker brought up Mr. Trump’s written responses and asked whether “his answers showed that he wasn’t always being truthful.” Rather than demurring as he had to similar questions, Mr. Mueller instead appeared to confirm her assessment, responding, “I would say generally.”
Both the lawmaker in July and Mr. Letter on Monday appeared to be referring in particular to the question of whether Mr. Trump lied about his campaign’s advance knowledge of and contacts with WikiLeaks about its possession of hacked Democratic emails and plans to publish them.
Mr. Trump wrote that he was “not aware during the campaign of any communications” between “any one I understood to be a representative of WikiLeaks” and people associated with his campaign, including his political adviser Roger J. Stone Jr., who was convicted at trial last week for lying to congressional investigators about his efforts to reach out to WikiLeaks and his discussions with the campaign.
“I do not recall discussing WikiLeaks with him,” Mr. Trump also wrote of Mr. Stone, “nor do I recall being aware of Mr. Stone having discussed WikiLeaks with individuals associated with my campaign.”
But the publicly available portions of the Mueller report suggest that evidence exists to the contrary. Several Trump aides, including Michael D. Cohen and Rick Gates, testified that they heard Mr. Trump discussing coming WikiLeaks releases over the phone. And in October 2016 Stephen K. Bannon, the campaign chairman, wrote in an email that Mr. Stone had told the campaign “about potential future releases of damaging material” by WikiLeaks shortly before it began publishing more hacked emails.
Mr. Letter brought up redactions in the report associated with Mr. Stone and a redacted reference to something that Paul Manafort, Mr. Trump’s former campaign chairman, had said to a grand jury.
“Manafort said that shortly after WikiLeaks’ July 22, 2016, released of hacked documents, he spoke to Trump [redacted]; Manafort recalled that Trump responded that Manafort should [redacted] keep Trump updated,” the Mueller report said, citing grand-jury material as the reason for the redactions.
The report went on to suggest that House investigators may see Mr. Manafort’s grand-jury testimony as potentially corroborating Mr. Gates’s account of Mr. Trump’s conversation with Mr. Stone about WikiLeaks.
“Deputy campaign manager Rick Gates said that Manafort was getting pressure about [redacted] information and that Manafort instructed Gates [redacted] status updates on upcoming releases,” the report said, citing an F.B.I. interview with Mr. Gates.
Mr. Letter told the court, “The Manafort situation shows so clearly that there is evidence, very sadly, that the president might have provided untruthful answers,” he said, adding that this might be part of impeachment.
The Mueller report cited additional evidence from Mr. Gates that Mr. Trump did have discussions about the content or timing of the future release of hacked emails.
For example, Mr. Gates also told investigators that about that same time, he was with Mr. Trump in a car trip to an airport when Mr. Trump received a call. After something that is redacted in the public version of the report, it recounts that after Mr. Trump hung up, he told Mr. Gates “that more releases of damaging information would be coming,” the report said.
Attorney General William P. Barr permitted the House Judiciary Committee to see most of the Mueller report, including portions that are redacted from the public version because they pertained to ongoing cases, but he has refused to let them see material that is subject to secrecy rules because it was presented to a grand jury.
In July, the House petitioned the chief judge of the Federal District Court for the District of Columbia, Beryl A. Howell, for an order that would permit it to gain access to that material too. Its court filings in that matter were the first time that it formally pronounced itself engaged in an impeachment inquiry; there is precedent, including in the Nixon Watergate scandal, permitting the House to get grand jury information for impeachment proceedings.
Judge Howell in October ruled that the House Judiciary Committee should be permitted to see the grand-jury material in the report and its underlying basis. The Justice Department appealed that ruling. The hearing on Monday centered on whether the appeals court should temporarily stay the district judge’s ruling while it considers that appeal.
Judge Neomi Rao, a former Trump White House official whom he recently appointed to the bench, asked questions suggesting she was sympathetic to the Justice Department’s position that allowing Congress to see material before the litigation is resolved would cause “irreparable harm.”
Judge Judith W. Rogers, a 1994 appointee of President Bill Clinton, asked questions suggesting she was sympathetic to the House’s argument that Judge Howell had already persuasively disposed of the issues so the Justice Department was going to lose, and that Congress had an urgent need to see the material without further delay.
The third judge on the panel, Thomas B. Griffith, a 2005 appointee of President George W. Bush, seemed interested in exploring whether Judge Howell ought to first issue an order permitting only a small number of House staff to see the raw materials, to allow for case-by-case arguments that the House needed to see particular bits of grand-jury evidence.