Washington DC - The former top US infectious disease official on Wednesday faced adversarial questioning from Republican senators about the origins of Covid-19, and on the advice of lawyers, invoked his constitutional right not to answer, casting the hearing as a character assassination.

It was the latest twist in the long-running feud between Anthony Fauci, who spent decades as the nation's top expert in infectious disease, and Republican Senator Rand Paul, who insists on unsubstantiated claims that the origins of the pandemic began in a lab and were covered up.

Paul, who chairs the Senate Committee on Homeland Security and Governmental Affairs, had subpoenaed the now-retired Fauci to testify, and prior to the hearing released thousands of pages of the immunologist's unredacted personal diary.

Citing Paul's "obsession" with him, Fauci said he would invoke the Fifth Amendment, refraining from answering questions to avoid self-incrimination, adding that it "pains me to do so."

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Fauci indicated his legal team believed Paul intended to entrap him in a slip-up that could result in perjury charges.

"The only conclusion I can reach is that the sole reason he is calling me before this committee is to get me to say something, anything, that could vindicate his repeated public pledges that I end up, in his words, quote 'behind bars,'" Fauci said.

Fauci (85) noted in his opening statement that he had testified before Congress more than 200 times over nearly four decades, saying "I proved that I believe in and respect the value of legitimate congressional oversight.

Paul began the hearing with a tirade against Fauci, repeating his accusations that the doctor directed the funding of research in China that triggered the spread of Covid-19 while the official was running the National Institute of Allergy and Infectious Diseases.

The senator has said Fauci lied about that to Congress, a claim without evidence that the public health expert has repeatedly denied.

Former President Joe Biden had given Fauci a preemptive pardon on January 19, 2025, but that applies only to actions taken prior to that date.

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President Donald Trump weighed in on Truth Social, saying Fauci's "ideas were CRAZY!" in the pandemic's early days.

Some lawmakers on the panel stated their disapproval with the proceedings, including Democratic Senator Gary Peters, who accused Paul of relitigation to "legitimize a predetermined conclusion that was reached years ago."

Senator Maggie Hassan, also a Democrat, said the hearing was designed to "entrap" Fauci.

Paul told Fauci that "there will be repercussions" for his use of the Fifth Amendment. When Fauci's lawyer, David Schertler, attempted to speak on his client's behalf, Paul ordered him removed from the room.

Democratic Senator Richard Blumenthal called the proceedings the result of a "vendetta" and a "show trial."

He also emphasized that invoking the Fifth Amendment was a protected right that must be "respected."