Anthony Fauci said he isn't worried about Senator Rand Paul's threats to investigate him should Republicans retake a majority in Congress next year.

'My records are an open book,' Dr. Fauci told CNN's New Day on Tuesday morning.

'They are talking about things that are really bizarre, like crimes against democracy by shutting down the government,' he continued. 'All I have ever done — and go back and look at everything I've ever done — was to recommend common sense, good, CDC-recommended public health policies that have saved millions of lives.'

The nation's top immunologist challenged: 'If you wanna investigate me for that, go ahead.'

His response comes after Republican Senator Paul of Kentucky threatened investigation.

'One way or another, if we are in the majority, we will subpoena his records and he will testify in the Senate under oath,' Paul said on Monday when speaking of Fauci.

Paul, an ophthalmologist before becoming a lawmaker, is in line to be chairman of the Senate Health, Education, Labor and Pensions Committee if Republicans win the majority. Republican Senator Richard Burr of North Carolina, the current ranking member, is retiring from the Senate. 

Earlier this year, Paul shared the same sentiment, saying: 'If we win in November, if I'm chairman of a committee, if I have subpoena power, we'll go after every one of [Fauci's] records.'

Fauci appeared on CNN Tuesday morning as he discussed the spread of Monkeypox in the U.S. and President Biden's recovery from COVID-19.

Paul and Fauci are no stranger to tiffs, with the two constantly sparring publicly over the last few years of the coronavirus pandemic.

Specifically, Paul has questioned Fauci over the origins of the virus and the gain-of-function research at the Wuhan Institute of Virology in China, which the senator claims is how COVID-19 came to be.

The Kentucky lawmaker has accused Fauci of somehow having some sort of involvement in the emergence of the virus because the National Institutes of Health granted funding to an organization conducting research at the Wuhan lab.

Fauci has repeatedly dismissed these claims.

Friday, however, the doctor said he now has 'an open mind' to the possibility that the virus was the result of a Chinese lab leak after repeatedly saying the most likely first emergence was an animal transmitting the disease to a human.

'We have an open mind but it looks very much like this was a natural occurrence, but you keep an open mind,' he told Fox News' Bret Baier in a Friday interview.

Baier grilled Fauci about a claim he made in April 2020, after being sent a link to a report made by Baier himself, that saw Fauci dismiss the lab leak theory as 'a shiny object that will go away.'

The Fox News anchor said: 'When you read the email from Kristian Andersen who says…'one has to look really closely to see some features (potentially) look engineered.'

'And you say this is a shiny object and it will go away. It does not look like you're open minded to it.'

Fauci appeared to try to deflect by flattering Baier, saying: 'Bret, I know you're a good person, I've known you a long time.'

'If you take a group of emails when people are considering and thinking out loud, and stop there, and don't look at the weeks of consideration by the same people who wrote the same emails… in published peer review literature, they explain why they thought it was a natural occurrence,' he added.

In February 2020, California-based virologist Kristen Andersen, speculated that COVID appeared to be genetically-engineered.