WATCH: Rand Paul says there's one thing Americans have never heard from Fauci

Dr. Anthony Fauci ran point as the COVID-19 explainer-in-chief under two different administrations, steering policy and messaging on the virus that rattled the country and world for years.

But there is one thing in all of his media appearances, profiles, interviews and congressional hearings that Sen. Rand Paul, R-Ky., contended Fauci never said: that he was sorry.

"I mean, I'd like to hear him say he's sorry," Paul said. "Can he say he is sorry for funding — the research was dangerous research in China? Almost everybody agrees with that."

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"Now he says, 'Oh, well, it didn't meet this definition or this definition, it was dangerous research," he continued. "It was a judgment error. It was a profound judgment error."

Paul and Fauci are set to square off Wednesday morning in the Homeland Security and Governmental Affairs Committee, the panel that Paul leads, in a clash that has been years in the making.

In the lead up to Wednesday’s hearing, Paul unveiled over 1,000 pages of Fauci’s diary, providing his own color commentary online about Fauci's motivations leading up to and during the pandemic.

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The lawmaker has had his sights set on Fauci since the beginning of the COVID-19 pandemic and accused him of funding research in China that led to the eventual outbreak of the virus.

And though Fauci has been out of the public spotlight since 2022, when he stepped down from his role as director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health (NIH), the two will finally get the chance to square up and settle the feud.

"I think he actually could do better in the hearing if he'd come forward and apologize for funding this research," Paul said. "No one's ever heard an apology from him. All they hear is sort of the idea that he never did anything wrong and that there's nothing wrong with that."

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Paul has said that the former chief medical advisor to the president deserves to be in prison for his alleged role in funding gain-of-function research, and warned that his pardon from former President Joe Biden wouldn’t hold up.

Notably, Fauci's former top advisor at the National Institute of Allergy and Infectious Diseases, Dr. David Morens, was indicted by the Justice Department earlier this year on charges of allegedly conspiring to evade public records laws, hide communications regarding the origins of COVID-19, and destroy federal records.

Gain-of-function research, or work that enhances a virus's transmissibility or lethality, and Fauci’s alleged role in funding that type of research through his position at the Wuhan Institute of Virology in China has been Paul’s focal point for years in his crusade against the former COVID-19 czar.

And he argued that the issue of researching the spread of a virus, or its killing potential, predates the pandemic.

Paul charged that in 2010, research conducted by Ron Fouchier, a Dutch virologist, produced a version of H5N1, commonly known as bird flu, that was transmissible "through the air between mammals."

"And half the scientific community said, ‘Oh my God, this could be the end of the world. We're doing this s---,’" Paul said.

"And Fauci was on the other side, and he said at the time in a Washington Post op-ed that even if a pandemic should occur from a scientist being bitten or somehow infected, the knowledge is worth the risk," he continued. "That needs to be debated by the country. Is the knowledge of creating viruses that could kill the world worth the risks? And I don't think it is."