Sen. Rand Paul (R-Ky.) once again confronted Dr. Anthony Fauci Thursday over National Institutes of Health funding for risky virus research in China and said it was time the White House's top COVID-19 adviser resign.

Fauci, the director of the NIH's National Institute of Allergy and Infectious Diseases, testified before the Senate on the Biden administration's pandemic response.

When it was time for Paul to ask questions, the Kentucky lawmaker began grilling Fauci over recent revelations that the NIH gave a grant award to the nonprofit group EcoHealth Alliance that then sub-awarded federal funding to the Wuhan Institute of Virology, where at least one gain-of-function research experiment was conducted in violation of the NIH grant's terms.

Gain-of-function research involves artificially engineering viruses to give them new attributes. The federal government restricts such research if it results in a virus becoming more transmissible or deadlier among humans. Previously, both Fauci and NIH Director Francis Collins have denied that the NIH ever funded research in China that made a virus deadlier to humans.

But documents reported by the Intercept last month revealed that using the NIH grant, EcoHealth Alliance funded gain-of-function experiments at the Wuhan lab that resulted in new chimeric viruses. One experiment made a chimera from the deadly MERS virus. Another combined two SARS-like bat coronavirus and infected genetically engineered mice with the altered viruses.

"I don't expect you today to admit that you approved NIH funding for gain-of-function research in Wuhan, but your repeated denials have worn thin and a majority of Americans, frankly, don't believe you," Paul said in his opening remarks.

"The facts are clear. The NIH did fund gain-of-function research in Wuhan despite your protestations," he stated.

WATCH: Complete exchange between Sen. @RandPaul and Dr. Anthony Fauci. \n\nFAUCI: "It makes me very uncomfortable to have to say something, but he is egregiously incorrect in what he says. Thank you."\n\nPAUL: "History will figure that out on its own."pic.twitter.com/5R7Auaylzv

— CSPAN (@cspan) 1636039693

Scientists have raised concerns that the SARS-CoV-2 virus, which caused the COVID-19 pandemic, was possibly engineered in the Wuhan lab and leaked from there. This theory, and the theory that the virus occurred naturally in animals and leaped to human beings, are the two dominant explanations for the origins of the virus, though there is no conclusive scientific evidence leaning toward either explanation.

Paul takes the side of the lab-leak theory, and during his time to speak, he said Fauci's repeated denials of funding gain-of-function research in Wuhan present a "clear and present danger to the country and to the world."

He accused Fauci of refusing to take responsibility for the coronavirus pandemic and of misleading the public by deflecting criticism of gain-of-function research and denying its possible role in the origins of COVID-19.

"You continue to support NIH money going to Wuhan. You continue to say you trust the Chinese scientist. You appear to have learned nothing from this pandemic," Paul said. "Will you today take some responsibility for funding gain-of-function research in Wuhan?"

"Senator, with all due respect, I disagree with so many of the things that you've said," Fauci replied.

He once again quibbled over the precise definition of "gain-of-function research," arguing that the Health and Human Services Department's framework for reviewing gain-of-function research proposals did not flag the EcoHealth Alliance project with the Wuhan Institute of Virology as a problematic gain-of-function experiment.

But Paul interrupted him and directly asked whether the NIH-funded experiment conducted by Chinese scientists — which involved combining the SHC014 bat coronavirus with the WIV1 SARS-like coronavirus into a new chimeric virus that made humanized mice sicker than the naturally occurring WIV1 virus — qualified as gain-of-function research.

Fauci began to respond by quoting the HHS framework and guidelines, but Paul interrupted again, accusing Fauci and the NIH of "defining away gain-of-function" by changing the NIH website's definition of that research so that Fauci's sworn testimony would not contradict the facts.

"This is terrible and you're completely trying to escape the idea that we should do something about trying to prevent a pandemic from leaking from a lab. The preponderance of evidence now points towards [COVID-19] coming from the [Wuhan] lab, and what you've done is change the definition on your website to try to cover your ass, basically," Paul charged.

"Until you accept responsibility, we're not going to get anywhere close to trying to prevent another lab leak of this dangerous sort of experiment. You won't admit that it's dangerous, and for that lack of judgement I think it's time that you resign," he finished.

Given some time to respond, Fauci said Paul's statements were an "egregious misrepresentation" and that he would not have time "to refute all of them."

But he did say, "I have no responsibility for the current pandemic." He also said most "card-carrying viral phylogeneticists and molecular virologists" would disagree with Paul's assertion that most scientific evidence supports the lab-leak theory. He also denied that the NIH continues to fund research at the Wuhan Institute of Virology.

"It makes me very uncomfortable to have to say something, but he is egregiously incorrect in what he says," said Fauci.

"History will figure that out on its own," Paul replied.