By Betsy Klein, CNN

(CNN) -- President Donald Trump revived his public criticism of Dr. Anthony Fauci Tuesday morning, continuing his efforts to undermine the infectious disease expert even as the doctor said he's not going to bow to pressure.

Trump contended in the tweet that Fauci's pitching arm -- a reference to his poor first pitch at Nationals Park -- is "far more accurate than his prognostications." Fauci's recommendations and assessments have largely been in line with public health experts throughout the coronavirus pandemic but not aligned with what the President perceives his political interests to be.

On Monday, Fauci said he is not deterred and will continue to serve in his role despite the criticism.

"I'm not going to walk away from this outbreak, no matter who's the president," Fauci told CNBC.

Trump and Fauci have previously sparred, the President contending that Fauci has "made a lot of mistakes" and Fauci openly questioning some of Trump's inaccurate claims during many television appearances.

Earlier this week, Fauci, the longtime director of the National Institute of Allergy and Infectious Diseases, slammed the Trump campaign for using his words out of context in a campaign advertisement touting Trump's pandemic response.

"In my nearly five decades of public service, I have never publicly endorsed any political candidate. The comments attributed to me without my permission in the GOP campaign ad were taken out of context from a broad statement I made months ago about the efforts of federal public health officials," Fauci said in a statement provided exclusively to CNN Sunday when asked if he agreed to be featured in the ad.

On Monday, Fauci warned during an appearance on CNN that if the campaign featured him in another ad, "That might actually come back to backfire on them." And, Fauci told the Daily Beast, "By doing this against my will, they are, in effect, harassing me."

"I mean obviously there are a lot of things that are going on that you would prefer did not happen, like the ad, which put me in a political context, which I spent my entire career staying out of political context. That's not helpful, but I'm certainly not going to give up. I've devoted my entire professional life to fighting infectious diseases," Fauci said in an interview on CNBC Monday.

Trump on Tuesday also referenced Fauci's advice given early in the pandemic against wearing masks. That decision was due largely to a nationwide shortage of masks. But the attempted criticism is particularly ironic given that Fauci has a high approval rating and Trump has used his likeness to appeal to voters.