Defense attorneys for onetime Trump campaign chairman Paul Manafort inadvertently revealed Tuesday that their client stands accused of sharing polling data with a suspected former Russian intelligence officer, according to court documents filed publicly in Washington D.C.

As part of a document meant to defend Manafort against accusations that he lied to federal prosecutors after signing onto a cooperation agreement with special counsel Robert Mueller, his defense counsel failed to adequately redact sections of their filing. Those sections were meant to remain secret and reflect information that has not previously been disclosed.

One passage that was meant to be redacted reveals that Mueller’s prosecutors, tasked with probing Russian meddling in the 2016 campaign, have accused Manafort of sharing 2016 campaign polling data with Konstantin Kilimnik, a longtime business associate whom the special counsel has identified as a former Russian intelligence officer.

“The Government’s allegation that Mr. Manafort lied about sharing polling data with Mr. Kilimnik related to the 2016 presidential campaign,” defense counsel wrote, was “not at the forefront of Mr. Manafort’s mind during the period at issue and it is not surprising at all that Mr. Manafort was unable to recall specific details prior to having his recollection refreshed.”

Special counsel prosecutors accused Manafort in November of breaking a plea deal by lying to the special counsel’s office. At a hearing in December, the federal judge overseeing Manafort’s case in Washington D.C. asked the government to provide some “underlying evidence” to support the scant details they’ve offered about the content of his alleged lies.

Mueller’s team and attorneys for Manafort agreed in court last month to conduct informal discussions about the alleged lies before defense counsel responded. At the time, Manafort’s team said they did not have enough information from the government about their client’s alleged lies to reply.

After leveling that accusation, prosecutors filed a heavily-redacted court document describing five areas in which Manafort is accused of lying to government investigators, including misleading statements about his contacts with Trump administration officials. He was also accused of lying about his interactions with Kilimnik and another unspecified Justice Department investigation.

But on Tuesday, Manafort’s team sought to rebut those accusations point by point.

“Mr. Manafort provided complete and truthful information to the best of his ability,” Manafort’s lawyers wrote. “He attempted to live up to the requirements of his cooperation agreement and provided meaningful cooperation relating to several key areas under current government investigation.”

Defense counsel for Manafort claim their client “did not recall having a conversation” with two Trump administration officials and that his recollection about contacts with Kilimnik is “unsurprising,” because “these occurrences happened during a period when Mr. Manafort was managing a U.S. presidential campaign and had countless meetings, email communications, and other interactions with many different individuals, and traveled frequently.”

Rep. Adam Schiff, D-Calif., chairman of the House Intelligence Committee, told ABC News that Tuesday’s revelation “raises more questions than answers.”

“The question is why? Why would Russians be interested in polling data on an American campaign? Why would that be of value? How would the Russians make use of that?” Schiff asked. “And of course one question above all is why did Manafort lie about it?”

With Democrats back in the majority in the House, Schiff said he plans to reinvigorate his panel’s investigation into possible Russian collusion, telling ABC News Tuesday he hopes to “get the answers to all these questions.”

Manafort was found guilty in August on eight counts of tax and bank-fraud in a Virginia case related in part to his work as an unregistered foreign lobbyist. Sentencing in that case – which could result in a lengthy prison term – is scheduled for next month.

In September, on the eve of a second trial in Washington, D.C., Manafort struck a plea deal with prosecutors that allowed him to plead guilty to lesser charges in exchange for “broad” cooperation.

But prosecutors in the Washington, D.C., case say he reneged on that agreement by lying during interviews.

Manafort is scheduled for sentencing in that case on March 5. But speculation that President Trump may consider pardoning his onetime campaign chairman has grown.

In November, asked by the New York Post about a possible pardon for Manafort, Trump said he “wouldn’t take it off the table.”

On Thursday, when a reporter asked, "Did you know Paul Manafort was sharing polling data from your campaign with the Russians? Trump responded, "No. I didn’t know anything about that."

ABC News' Benjamin Siegel contributed to this report.