"Under the advice of my attorneys, I will invoke my right under the Fifth Amendment of the Constitution to refrain from answering your questions," Fauci told the Senate Homeland Security and Governmental Affairs Committee, in his opening statement on Wednesday.
Fauci declined to answer 15 questions from Republican Senator Rand Paul, invoking his Fifth Amendment rights for each of them.
Paul said Fauci was not allowed to plead the Fifth, that a pardon issued by former president Joe Biden would not protect him, and that there would be consequences for his refusal to answer the questions.
Fauci, who led the National Institute of Allergy and Infectious Diseases for 38 years and became the face of the US COVID pandemic response, long has been the target of criticism by President Donald Trump and many American conservatives.
Trump before the hearing wrote of Fauci on social media: "His ideas were CRAZY!"
Biden pardoned Fauci on January 19 2025, for any offences he may have committed since 2014 in connection with COVID-19 or in his role as director of the National Institute of Allergy and Infectious Diseases. The pardon does not cover subsequent conduct.
Paul had one of Fauci's lawyers removed from the hearing after refusing to recognise his attempts to speak.
In a statement, Fauci's attorney David Schertler called Paul's pursuit "an obsessive vendetta" and said the accusations "are false and disgraceful, and we will examine all options to hold him accountable".
Paul has for years called for Fauci to be indicted and accused him of lying to Congress about whether the National Institutes of Health (NIH) funded "gain-of-function" research in Wuhan, China, and of helping cover up the origins of COVID-19.
Fauci denies both claims and says he has testified truthfully multiple times before Congress on these issues.
Gain-of-function research is, broadly, work that modifies a pathogen in ways that could make it more transmissible or dangerous, though scientists disagree over how narrowly the term should be defined.
That disagreement is the crux of the Paul-Fauci dispute: Paul says the NIH funded such work in Wuhan and that Fauci lied when he denied it, while Fauci says the research did not meet the government's formal regulatory definition.
COVID-19's origins remain unresolved. The FBI said in 2023 that a leak from a laboratory in the central Chinese city of Wuhan likely caused the pandemic, a claim China said had "no credibility whatsoever".
The CIA in January 2025 said it had shifted its assessment and concluded a lab leak was likely, but with "low confidence," while four other US intelligence agencies and the National Intelligence Council believe the virus most likely emerged via natural transmission.
Paul this week published a 1141-page tranche of Fauci's pandemic-era diary entries, spanning December 2019 through December 2022.
"Many entries in Fauci's daily historical account completely undermine the official narrative that Fauci and other public health officials espoused," he said in a statement.
A fact-check document provided by a representative of Fauci said the diary entries match what he said publicly at the time.
He has said since 2021 he kept an "open mind" that COVID could have leaked from a lab, and spoke publicly in early 2020 about asymptomatic transmission and China's lack of transparency, the very matters Paul says the diary reveals.
Paul has for years pledged to see Fauci imprisoned.
The entries largely chronicle Fauci's media appearances and fame. A review of his public record provided by a representative of Fauci shows his positions were consistent with the diary.
The Trump administration issued a policy on Tuesday barring federal funding for "dangerous gain-of-function" research, the category at the heart of the Fauci dispute.
