Former White House Chief of Staff Ron Klain revealed to House investigators that both Hillary Clinton and National Security Adviser Jake Sullivan expressed concerns about President Joe Biden’s political viability months before he ended his re-election campaign.

Klain, who served as Biden’s top aide during the first half of his term, met with staff on the House Oversight Committee for over five hours Thursday as part of an ongoing Republican-led investigation into whether top Biden officials concealed evidence of cognitive decline while he was in office.

A source familiar with the transcribed interview told Fox News that Klain stood by his view that Biden was mentally capable of serving as president and not too old to run again. However, Klain reportedly said that both Clinton and Sullivan had privately approached him in 2024, urging him to reconsider Biden’s chances of winning re-election.

According to the source, Sullivan told Klain that Biden was “less effective in 2024 compared to 2022.”

Clinton’s involvement marks one of the most significant behind-the-scenes criticisms from within the Democratic establishment. The former Secretary of State and 2016 presidential nominee is said to have voiced these concerns before Biden’s disastrous June 2024 debate performance, which preceded his decision to step aside from the 2024 race the following month.

Sullivan, who served in senior roles under both Biden and Clinton, has denied the account. “Jake did not have a conversation with Ron about Joe Biden running for president before the debate,” said Adrienne Watson, a spokesperson for Sullivan, in a statement to Fox News.

During his interview, Klain also acknowledged Biden had become “less energetic” and increasingly forgetful, according to the source. “Mr. Klain stated that President Biden often confused names and proper nouns, and it got worse over time,” the source said. Despite his other statements, Klain defended Biden’s “acuity to govern.”

He reportedly added that there was no reason to doubt President Donald Trump’s mental fitness, either.

Klain’s testimony came as part of House Oversight Chairman James Comer’s probe into whether Biden’s staff used an autopen to sign executive actions without his awareness and whether they misled the public about his condition. Comer (R-KY) said Klain was “fairly responsive,” adding that during the interview there were “tidbits” of new information. “Evidence emerges on a daily basis that would suggest Joe Biden wasn’t mentally fit to be President of the United States,” Comer said.

Despite the politically charged nature of the inquiry, lawmakers from both parties praised Klain’s demeanor and cooperation. Rep. Andy Biggs (R-AZ) told Fox News, “I think he is telling what he knows accurately.” Democratic Rep. Ro Khanna of California agreed, stating, “He answered every single question. He was fully cooperative.”

Klain is the sixth former Biden administration aide to testify over the course of the investigation and the third to do so voluntarily. Previous witnesses included White House physician Dr. Kevin O’Connor and senior advisor Anthony Bernal, who both appeared under subpoena and invoked the Fifth Amendment.

Longtime Biden aide Ashley Williams and former staff secretary Neera Tanden also gave voluntary testimony. Jeff Zients, Biden’s second chief of staff, has also been asked to testify.

Klain, a longtime Democratic operative and debate prep strategist, played a key role in Biden’s preparation for what became his campaign-defining 2024 debate against Donald Trump. He remained silent when arriving at and departing from the Capitol, declining to speak with reporters.