Ex-President Joe Biden's former chief of staff Ron Klain told House investigators that Hillary Clinton approached him with concerns about the octogenarian leader's political viability "by 2024," Fox News Digital has learned.
Klain spoke with staff on the House Oversight Committee for over five hours on Thursday, as Committee Chairman James Comer, R-Ky., continues to probe whether top Biden aides concealed signs of mental decline in the ex-president.
A source familiar with his voluntary interview told Fox News Digital that Klain believed Biden was mentally sharp enough to serve as president, and was not too old to run.
But the ex-secretary of state and former Biden national security adviser Jake Sullivan both "approached Ron Klain stating they believed Joe Biden was not politically viable" months before he dropped his re-election bid in July 2024, the source said.
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Sullivan told Klain that Biden "was less effective in 2024 compared to 2022," the source said.
It's not immediately clear if Biden's mental acuity was the reasoning for their doubts, nor if they made the case to Klain together or separately.
But it's a significant indictment coming from top national Democrats of Biden in general, long before concerns about his fitness for office within the party were made public knowledge.
Sullivan had been a top aide to both Biden and Clinton, having served as the latter's senior policy advisor during her 2016 campaign.
Klain, who served as White House chief of staff for the first half of Biden's term, conceded that the then-president was less energetic and more forgetful, though he defended his "acuity to govern," the source said.
"Mr. Klain stated that President Biden often confused names and proper nouns, and it got worse over time," the source said.
Fox News Digital was told that Klain also said there was no reason to doubt President Donald Trump's own mental fitness.
Klain said nothing to reporters when going in or out of the committee room Thursday.
He's the sixth former Biden administration aide to appear for Comer's probe.
And despite the interview being largely staff-led, Comer did make an appearance for the early half of the sit-down, and Reps. Andy Biggs, R-Ariz., and Ro Khanna, D-Calif., were both briefly there as well.
Both Biggs and Khanna called Klain "credible" from what they saw inside the room.
"I think he is telling what he knows accurately," Biggs told Fox News Digital.
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On the other side of the aisle, Khanna told reporters, "He answered every single question. He was fully cooperative."
Three other former Biden White House aides who previously appeared – Annie Tomasini, Anthony Bernal, and ex-White House doctor Kevin O'Connor – all appeared under subpoena and pleaded the Fifth Amendment to avoid answering questions.
Longtime Biden aide Ashley Williams and ex-staff secretary Neera Tanden, like Klain, came for voluntary transcribed interviews.
Jeff Zients, who served as Biden's chief of staff for the final two years, was also asked to sit for a transcribed interview, a committee aide previously told Fox News Digital.
A source familiar with the Biden team's thinking previously called Republicans' probe "dangerous" and "an attempt to smear and embarrass."
"And their hope is for just one tiny inconsistency between witnesses to appear so that Trump’s DOJ prosecute his political opponents and continue his campaign of revenge," that source said.
When reached for comment, Adrienne Watson, a representative for Sullivan, told Fox News Digital, "Jake did not have a conversation with Ron about Joe Biden running for president before the debate."
Fox News Digital also reached out to Klain's attorney as well as a contact for comment for Clinton but did not hear back by press time.