Sen. Rand Paul of Kentucky subpoenaed Fauci to appear before a Senate committee Wednesday. It’s part of Paul’s yearslong accusations that the now-retired infectious disease expert had lied about the pandemic, something Fauci has called “preposterous.”

Leading up to the hearing, Paul released more than a thousand pages of Fauci’s personal diary covering the pandemic years. Pointing to some notes about early efforts at understanding how the virus emerged, Paul wrote on the social media platform X that what Fauci “wrote privately and what he told the country are two different stories.”

Some of the diary entries — including his uncertainty in the pandemic’s earliest days as scientists around the world raced to understand the new virus and how best to curb it before vaccines could be created — already were reflected in Fauci’s 2024 memoir and in interviews at the time.

But they’re likely to further inflame a partisan divide that, years after the pandemic, still makes Fauci a target of vitriol from people who blame him for mask mandates and other policies they believe infringed on their rights as hundreds of thousands of people were dying.

In an earlier letter to Paul, Fauci’s attorneys called his allegations “absolutely baseless” and part of an “obsessive and groundless vendetta.”

Scientists scrambled to Fauci’s defense ahead of the unusual hearing — the second time the longtime National Institutes of Health scientist has been back before Congress to discuss pandemic origins since leaving the government in 2022. While the COVID-19 pandemic introduced him to millions of Americans, he talked the nation through numerous outbreaks over decades, including HIV, Ebola and the 2001 anthrax attacks, while advising seven presidents.

In a public letter, more than 150 infectious disease experts and other scientists wrote that “no credible evidence has been produced to support these absurd charges” and that they are “urging our elected representatives in Congress stop these witch-hunts.”

The expected crux of Wednesday’s hearing: whether NIH-funded research in China may have played any role in how the pandemic started.

Many scientists believe the virus most likely emerged in nature and jumped from animals to people, coming to light when it spread at a wildlife market in the Chinese city of Wuhan. There’s no new scientific information supporting that the virus might instead have leaked from a laboratory, a theory Paul champions. A GOP-led subcommittee that studied the question in 2024 did not find any evidence linking Fauci to wrongdoing.

Fauci has long said publicly that he was open to both theories, but that there’s more evidence supporting COVID-19’s natural origins, the way other deadly viruses including coronavirus cousins SARS and MERS jumped into people.

Republicans also have accused Fauci of lying about whether his agency funded “gain of function” research — the practice of enhancing a virus in a lab to study its potential real-world impact — at a lab in Wuhan.

NIH for years gave grants to a New York nonprofit called EcoHealth Alliance that used some of the funds to work with a Chinese lab studying coronaviruses commonly carried by bats. But the definition of “gain of function” covers both general research and especially risky experiments to “enhance” the ability of potentially pandemic pathogens to spread or cause severe disease in humans. Fauci has previously stressed he was using the risky experiment definition and that “it would be molecularly impossible” for those bat virus experiments to have turned into the pandemic virus.

The Trump administration last year paused some federally funded gain-of-function research and on Tuesday announced new rules to tighten oversight.

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