Paul has repeatedly argued that Covid probably leaked from China’s Wuhan Institute of Virology – a theory that the CIA backed last year.

In the hearing, the senator suggested that while Fauci had said publicly that Covid originated naturally, his diaries indicated he privately believed the virus originated in a medical lab.

Republicans asked Fauci about shifting health guidance, which changed during the pandemic as health officials learned more about the disease. Fauci has previously defended his policy positions.

But several Democrats came to Fauci’s defence, including Senator Maggie Hassan, who said the hearing was “designed to entrap” him.

President Trump, meanwhile, took to social media to call Fauci “crazy”.

“I said from the beginning that the Virus came from the Wuhan Laboratory in China. Fauci strongly disagreed, always trying to protect China,” he said.

The World Health Organization said last year the natural-origin theory – the virus spilling over from animals to people – was the “best supported” idea from available evidence, but that until more information emerges, the matter is “inconclusive”.

Fauci has faced death threats during and after the coronavirus pandemic. Trump last year removed his security protection.

The former top health official was one of the most trusted members of the US government during its response to the pandemic as scientists were trying to learn about the virus as quickly as possible.

He was not always at loggerheads with Trump. In 2021, Trump awarded Fauci a presidential commendation for his work on the US Covid vaccine project, known as Operation Warp Speed.