Dr. Anthony Fauci accused Sen. Rand Paul (R-Ky.) of an “unhinged obsession” on Wednesday as he invoked the Fifth Amendment at least 100 times during a Senate hearing, declining to answer questions about Covid-19 origins and related research. The appearance came despite a broad pardon issued to Fauci by former President Joe Biden in the final hours of his administration, setting up a clash over how far that pardon extends and what it does not cover.

Fauci opened the hearing with a pointed statement, saying Paul was weaponizing the proceeding against him. He cited Paul’s “obvious obsession with calling for my prosecution, his repeated slanderous comments about me,” and the senator’s decision to publicly release more than 1,000 pages of Fauci’s personal pandemic-era diary over the preceding weekend.

Biden’s preemptive, unconditional pardon covered any offenses connected to Fauci’s NIAID directorship and pandemic-response roles over a 10-year period from January 1, 2014, through January 19, 2025. But Republicans on the Senate Homeland Security and Governmental Affairs Committee argued that the pardon does not shield Fauci from questions about his testimony now, and that he may be trying to exploit that distinction by refusing to answer. The hearing quickly became less about Fauci’s past public-health decisions and more about whether a witness can avoid self-incrimination while still facing congressional questioning tied to the same period.

House Oversight Committee Chairman James Comer told Fox News that “Biden’s pardon doesn’t cover Dr. Fauci’s testimony this week and if he continues to lie, he must be held accountable.”

“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 that could vindicate his repeated public pledges that I end up, in his words, ‘behind bars,'” Fauci said. He added that “any reasonable person who has followed his unhinged obsession with me would readily come to the same conclusion.” Fauci said invoking the Fifth “pains” him because of his “decades-long record of cooperating with Congress,” but that he was acting on the advice of his lawyers.

Republicans challenge the legal basis

Sen. Josh Hawley (R-Mo.) directly questioned Fauci’s constitutional argument, telling him he does not have Fifth Amendment rights because of Biden’s pardon. Hawley cited the 1896 Supreme Court precedent Brown v. Walker in arguing that a pardoned witness cannot “stand upon his privilege.”

Paul also warned that Fauci’s Biden-era pardon “will not shield him from legal action for obstructing Congress,” and said the panel would consider next steps, including a possible contempt referral, after Fauci refused to answer dozens of questions on gain-of-function funding, Wuhan lab oversight, and coordination with the intelligence community. That could make the hearing a test case for how Congress handles a witness who is protected from prosecution for past conduct but still declines to engage on matters lawmakers say fall within their oversight authority.

The hearing took a dramatic turn when Paul ordered Fauci’s attorney, David Schertler, removed from the room after Schertler repeatedly tried to speak without being recognized. Paul noted that Fauci still had “the advice of the other half a dozen attorneys” he brought with him.

Questions Fauci refused to answer

Fauci declined to respond to a series of recurring issues raised during the hearing, including:

• The rationale for NIH funding of coronavirus research at the Wuhan Institute of Virology and whether it met the definition of gain-of-function work.
• Whether the CIA transferred funds to NIH, or whether NIH coordinated research with intelligence agencies.
• Whether he still supports his past defense of Ron Fouchier’s ferret-transmissible avian flu experiment, in which Fauci wrote that “even if a pandemic should occur, the knowledge is worth the risks”.
• Whether he was aware of alleged gain-of-function work on monkeypox at Fort Detrick or any classified biodefense special-access programs.

Political backdrop

The hearing comes amid renewed scrutiny of pandemic-origin theories. U.S. intelligence agencies including the CIA, FBI and Department of Energy have assessed a lab-origin explanation as “more likely than not,” while a 2024 House GOP subcommittee said it found no direct evidence that Fauci acted improperly.

Paul, who has publicly said Fauci belongs in prison, now faces a decision on whether to pursue contempt or obstruction proceedings — a move that would test whether a presidential pardon can protect a witness who refuses to answer a lawfully issued subpoena.

For this story, Fortune journalists used generative AI as a research tool. An editor verified the accuracy of the information before publishing.

This story was originally featured on Fortune.com