After Sen. Rand Paul, R-Ky., sent letters to 15 federal agencies requesting information on their purported newfound connections to a 2018 grant proposal that sought to experiment with a COVID-19-type microbe, the lawmaker told Fox News the development is the "smoking gun" critics had long sought.

Paul claimed the developments — to which he credited a Marine Corps whistleblower — tie the National Institutes of Health to the research and proves former National Institute of Allergy & Infectious Diseases Director Anthony Fauci was untruthful in his denials before Congress.

The lawmaker, a doctor of ophthalmology who has been investigating COVID-19's origins since the height of the pandemic, blasted the feds for allegedly keeping the research from the public.

"Yeah, we found out about this first from a brave Marine who reported that this research — was a grant proposal back in 2018 — would have allowed Wuhan Institute to create a virus very similar to what COVID-19 turned out to be," he said.

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"But we only found out about this from a whistleblower — nobody else in government ever informed us, including Anthony Fauci."

Paul has long sparred with Fauci, who joined NIH in 1968, was appointed by former President Reagan to lead the NIAID and retired in December 2022.

During a July 2021 hearing before a Senate committee, Fauci bristled at Paul's claim he had lied about funding or being linked to funding gain-of-function research.

"Sen. Paul, I have never lied before Congress and I do not retract that statement. This paper that you are referring to was judged by qualified staff up and down the chain as not being gain-of-function," Fauci said at the time. "Sen. Paul, you do not know what you are talking about, quite frankly."

In an op-ed for Fox News Digital, Paul wrote that he requested information from 15 agencies, including Fauci's former employers NIAID and NIH, about a 2018 grant proposal led by EcoHealth Alliance called "DEFUSE Project."

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Paul said the proposal was submitted to the DoD's research agency, DARPA, and that NIAID's Rocky Mountain Laboratories in Hamilton, Mont., was listed as a proposal partner at one point. In his missives, Paul requested each agency provide more information to him by April 23.

Paul told "America Reports" that when Fauci was asked about the DEFUSE grant, he claimed he did not fund it or "know anything about it."

"This was his own agency," the lawmaker added. "We now have proof that the NIH and the NIAID — Fauci's agency — knew about this proposal and were part of the proposal, despite him continuing in public to say he knew nothing of this proposal. This basically is a smoking gun that ties Anthony Fauci and NIH to the funding of research that may well have led to COVID-19."

Paul said DEFUSE was never funded by the feds, but that Fauci and others knew that the Wuhan lab continued to work on the microbial research.

"Anthony Fauci, for the first several months and really for years, has tried to call anybody who believes that it came from the lab or looks at evidence that the virus came from this lab, calls them conspiracy theorists, downplays them, denigrates them," he said.

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"He promoted journal articles to downplay and say it wasn't possible, when all the while it looks like he knew it."

Paul said that advising the public about the research could have led to more substantive understanding of the viability of the lab-leak theory. 

Many Americans had been lambasted for months over banter about the theory, which appeared to break the political barrier when liberal comic Jon Stewart stunned his former protégé Stephen Colbert by openly musing about a lab leak in February 2023.

When Stewart appeared on Colbert's CBS program, he quipped that "the disease is the same name as the lab," and that people should pause if they believe the virus sprang up when a "pangolin kissed a turtle," or "a bat flew into the cloaca of a turkey… "

Colbert replied by joking he must be working for Sen. Ron Johnson, R-Wis. — a supporter of the lab-leak theory.

The NIH confirmed in a statement to Fox News Digital it had received Paul's letter and would be responding directly. The NIAID did not respond to a separate request for comment.