United States President Donald Trump slammed top government scientist Anthony Fauci by suggesting the highly respected and popular doctor was an "idiot" and past his prime.

Trump did so in a call with campaign staffers on Monday, Oct. 19.

"People are tired of Covid," Trump told his campaign team in a call with several members of the press present.

"People are saying, 'Whatever -- just leave us alone.' They're tired of it. People are tired of hearing Fauci and all these idiots," the president said, which was quoted by multiple U.S. media.

"He's been here for, like, 500 years," Trump complained of Fauci, who is recognised worldwide for his work directing the National Institute of Allergies and Infectious Diseases in suburban Washington.

"Fauci, if we listened to him, we'd have 700,000, 800,000 deaths," Trump claimed on the call, before saying that it would be counterproductive to fire him before the presidential election Nov. 3.

Who is Anthony Fauci?

Fauci is a key member of the White House coronavirus task force.

He has served under six presidents, including Trump.

However, the 79-year-old distinguished doctor has increasingly been on the receiving end of the president's frustration.

Trump has been trying to shape the messaging on the much-criticised federal response to the pandemic.

In another interview with media, Trump also claimed that Fauci has made "bad calls" and he has been around for "350 years":

Defence of Fauci

Republican Senator Lamar Alexander came to Fauci's defence.

"Dr. Fauci is one of our country's most distinguished public servants. He has served 6 presidents, starting with Ronald Reagan," Alexander tweeted.

"If more Americans paid attention to his advice, we'd have fewer cases of Covid-19, & it would be safer to go back to school & back to work & out to eat."

Back-and-forth

Trump's name-calling came a week after Fauci expressed displeasure at the use of a clip of him in a Trump campaign video about the coronavirus.

"In my nearly five decades of public service, I have never publicly endorsed any political candidate," the immunologist said his statements in the video were taken out of context.

Fauci has at various points during the pandemic response clarified or corrected Trump's public comments on the development of Covid-19 treatments and vaccines.

The tone between them has sometimes been tense.

In April, Trump retweeted a post that contained the hashtag #FireFauci, before reassuring the people that "Tony" was doing a great job.

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Top photo via Reuters & Good Morning America