AMNA NAWAZ: Today, a special House subcommittee looking into the origins of the COVID-19 pandemic pressed the man who helped lead the nation's response, Dr. Anthony Fauci, the former head of the National Institute for Allergies and Infectious Disease.

William Brangham looks at some of the key criticisms leveled at Fauci's leadership during the pandemic and how he responded today.

DR. ANTHONY FAUCI, Former Chief Medical Adviser to President Biden: Thank you for this opportunity to testify.

WILLIAM BRANGHAM: The man who was the face of America's COVID response, Dr. Anthony Fauci, returned to Capitol Hill today to publicly answer a barrage of accusations, first, that he used his influence as the head of one of the American government's biggest grant-giving organizations to dictate what researchers said publicly about how the pandemic began, about whether it jumped into humans from a wild animal being sold at a Chinese food market in Wuhan or whether it came from an accidental leak out of the Chinese-run Wuhan Institute of Virology, which was researching coronaviruses.

DR. ANTHONY FAUCI: The accusation being circulated that I influenced these scientists to change their minds by bribing them with millions of dollars in grant money is absolutely false and simply preposterous.

WILLIAM BRANGHAM: Fauci also faced questions about whether NIAID's past grants to a virus researcher named Peter Daszak, who's president of the EcoHealth Alliance, was supporting research in China about how to make coronaviruses more contagious and virulent.

Representative Ronny Jackson, Republican of Texas, accused Fauci of funding the creation of the pandemic.

REP. RONNY JACKSON (R-TX): It was obvious to everyone that you and your organization, NIH, had a lot to lose if the American people were to discover that COVID-19 was most likely leaked from a lab in Wuhan, China, and that you via EcoHealth Alliance and Peter Daszak actually funded this research.

But during supportive questioning from Democrats, including Representative Raul Ruiz of California, Fauci said NIAID did not fund that kind of risky research and said that the viruses Daszak was studying couldn't have been responsible for what became SARS-CoV-2.

DR. ANTHONY FAUCI: Those viruses were phylogenetically so far removed from SARS-CoV-2 that it is molecularly impossible for those viruses to have evolved or being made into SARS-CoV-2.

It's just a virological fact.

WILLIAM BRANGHAM: But two weeks ago, under pressure from House Republicans, the Biden administration announced it would suspend grants to Daszak's organization, alleging it had failed to adequately monitor and report on its work in Wuhan.

Later in the day, Fauci did acknowledge under repeated pressure from lawmakers like Representative James Comer of Kentucky that one of his senior advisers, David Morens, violated numerous policies by using private e-mail-in altering documents.

Representative Jackson also pointed to an e-mail where Morens said Fauci, referred to here as Tony, also used private e-mail to skirt disclosure laws.

REP. RONNY JACKSON: Dr. Morens wrote to Dr. Daszak in April of 2021 -- quote -- P.S., I forgot to say, there is no worry about FOIAs.

I can either send stuff to Tony on his private e-mail or hand it to him to work or at his house.

He is too smart to let colleagues send him stuff that could cause trouble."

WILLIAM BRANGHAM: Fauci said he didn't know why Morens wrote that and insisted he never discussed COVID policy using his private e-mail.

At other times today, Fauci also faced criticism for promoting various public health measures.

Republican Brad Wenstrup of Ohio is chairman of the committee.

REP. BRAD WENSTRUP (R-OH): Dr. Fauci, you oversaw one of the most invasive regimes of domestic policy the U.S. has ever seen, including mask mandates, school closures, coerced vaccination, social distancing of six feet and more.

WILLIAM BRANGHAM: In previous testimony, Fauci said the CDC's initial guidance on maintaining six feet of distance wasn't -- quote -- "based in science," but based on earlier understanding of how far viral droplets could travel through the air.

He tried to clarify that statement today.

DR. ANTHONY FAUCI: Well, when I say was not based in science, I meant a prospective clinical trial to determine whether six foot was better than three was better than 10.

REP. JOHN JOYCE (R-PA): But once we realized that the virus was not spared by droplets and was aerosolized, did you feel an indication to go back to the CDC and said, let's base this on science?

REP. MARJORIE TAYLOR GREENE (R-GA): Children, children all over America were forced to wear masks.

WILLIAM BRANGHAM: Fauci also faced a fierce attack from Georgia Republican Marjorie Taylor Greene.

She was later admonished by her chairman.

REP. MARJORIE TAYLOR GREENE: We should be writing a criminal referral because you should be prosecuted for crimes against humanity.

You belong in prison, Dr. Fauci.

WILLIAM BRANGHAM: Earlier in the hearing, Fauci seemed to get choked up describing how those kinds of accusations often led to violent threats.

DR. ANTHONY FAUCI: It is very troublesome to me.

It is much more troublesome because they have involved my wife and my three daughters.

REP. DEBBIE DINGELL (D-MI): At these moments how do you feel?

Keep your mic on.

DR. ANTHONY FAUCI: Terrible.

REP. DEBBIE DINGELL: Do you continue to receive threats today?

DR. ANTHONY FAUCI: Yes, I do.

Every time someone gets up and says I'm responsible for the death of people throughout the world, the death threats go up.

WILLIAM BRANGHAM: Next week, former CDC Director Rochelle Walensky will testify before the same committee.

For the "PBS NewsHour," I'm William Brangham.