David Axelrod, a former senior adviser to President Barack Obama, said Wednesday that Robert Mueller did not look as "sharp" as he used to during a House Judiciary Committee hearing, calling the performance "painful."
"This is delicate to say, but Mueller, whom I deeply respect, has not publicly testified before Congress in at least six years. And he does not appear as sharp as he was then," Axelrod wrote.
"And it helps explain why Mueller wanted his aide nearby."
He later followed up with another tweet, saying, "This speed-dating approach to questions is hard on Mueller" and called it "painful" to watch.
"Not a commentary on the content. The report is damning. That was reenforced today. He has been an exemplary public servant, as people are both sides attested, but he clearly was struggling today and that was painful," Axelrod added.
Axelrod's criticism came as others expressed similar views of Mueller's answers. "Fox News Sunday" anchor Chris Wallace said the hearing had turned into a "disaster" for Democrats and for the former FBI director's reputation.
"He has seemed very uncertain with his brief. He doesn't seem to know things that are in the report," Wallace told Bret Baier and Martha MacCallum during Fox News Channel's all-day coverage of the House hearings.
Mueller was frequently tripped up and forced to ask lawmakers to repeat their questions during his rapid-fire questioning on Capitol Hill, though he reportedly prepared at length for the hearings.
At one point, he even said he wasn't familiar with Fusion GPS, the opposition research firm behind the controversial anti-Trump dossier.
The longtime lawman was known to be reluctant to testify, having made clear he would largely stick to the boundaries of his original report. He reiterated Wednesday that his testimony before House committees would be based on the text of his report on Russian election interference and potential obstruction of the investigation.
Fox News' Ronn Blitzer contributed to this report.