Mr. Corsi, a conspiracy theorist and friend of Roger J. Stone Jr., a former Trump adviser, recently told reporters that he refused an offer from the special counsel to sign a plea agreement saying that he willfully lied when he spoke to investigators.

“If I have to go to jail for the rest of my life, so be it,” Mr. Corsi told ABC News on Monday. “Have at it. I will not tell a lie to a federal judge or anybody else. They will not get me to commit a crime.”

Sarah Huckabee Sanders, the White House press secretary, deflected questions on Tuesday about Mr. Trump’s perspective on the special counsel’s accusation that Mr. Manafort lied to investigators. She said she was not aware of any discussions about a potential presidential pardon for Mr. Manafort.

Ms. Sanders repeated the White House position on the continuing investigation, saying, “the president was involved in no wrongdoing, was not part of any collusion.”

Mr. Trump recently provided written answers to some of Mr. Mueller’s questions about whether any of his associates coordinated with Russia’s efforts to interfere in the 2016 presidential election.

Mr. Manafort’s lawyers on Monday disputed that he lied to federal investigators and said he had met repeatedly with the special counsel’s office and answered questions truthfully as part of his agreement to cooperate with the investigation.

Facing a steep prison sentence for multiple criminal charges, Mr. Manafort signed a guilty plea agreement in September to two counts of conspiracy related to his consulting work in Ukraine. Lying to prosecutors during his subsequent cooperation violates that agreement and could lead to the special counsel pursuing additional charges against him.