The angry comments from the usually unflappable Fauci came after Paul repeatedly inquired about a National Institutes of Health–funded study that he alleges shows the organization funded research that could have contributed to the pandemic.

In May, Fauci denied that the NIH funded research at a lab in Wuhan, China, which some believe was the source of the virus. Paul didn’t quite call Fauci a liar, but certainly came close in his line of questioning Tuesday. He cited a paper that discusses gain-of-function research, which makes pathogens more transmissible in an effort to predict emerging diseases.

Fauci pushed back strongly, saying the paper Paul referred to had been “judged by qualified staff up and down the chain as not being gain of function.”

“You are implying that what we did was responsible for the deaths of individuals,” said Fauci. “I totally resent that. And if anybody is lying here, Senator, it is you.”

Fauci, along with Centers for Disease Control and Prevention Director Rochelle Walensky, are appearing before the Senate Health, Education, Labor, and Pensions (HELP) Committee. The official subject of the hearing is “The Path Forward” out of the pandemic, but they’re expected to face many questions about the Delta variant and whether new health measures, such as mandated mask wearing, will be necessary.