COLUMBUS, Ohio — When Jane Timken kicked off an eight-week advertising campaign on the Fox News Channel in her bid for the Republican nomination for Senate, she did not focus on immigration, health care or the economy. Her first ad was titled “Fire Fauci.”

Her target — Dr. Anthony S. Fauci, President Biden’s top medical adviser for the coronavirus — is also under attack in Pennsylvania, where Mehmet Oz, a television doctor who has entered the Republican Senate primary there, calls him a “petty tyrant.” Dr. Oz recently ran a Twitter ad calling for a debate — not between candidates, but between him and Dr. Fauci.

In Florida, Gov. Ron DeSantis released an advertisement last month telling Dr. Fauci to “pound sand” via the beach sandals the governor’s re-election campaign is now selling: “Freedom Over Fauci Flip-Flops.” In Wisconsin, Kevin Nicholson, a onetime Democrat running for governor as a conservative outsider, says Dr. Fauci “should be fired and referred to prosecutors.”

Republican attacks on Dr. Fauci are not new; former President Donald J. Trump, irked that the doctor publicly corrected his falsehoods about the virus, called him “a disaster” and repeatedly threatened to fire him. Senator Rand Paul, Republican of Kentucky, has grilled Dr. Fauci in nationally televised hearings, and Dr. Fauci — true to his fighter-from-Brooklyn roots — has punched back.

But as the 2022 midterm elections approach, the attacks have spread across the nation, intensifying as Dr. Fauci draws outsize attention in some of the most important state and local races on the ballot in November.

The Republican war on Dr. Fauci is partly a sign of Mr. Trump’s strong grip on the party. But Dr. Fauci, both his friends and detractors agree, has also become a symbol of something deeper — the deep schism in the country, mistrust in government and a brewing populist resentment of the elites, all made worse by the pandemic.

And Dr. Fauci, whose perpetual television appearances have made him the face of the Covid-19 response — and who is viewed by his critics as a high-and-mighty know-it-all who enjoys his celebrity — seems an obvious person to blame.

“Populism is essentially anti: anti-establishment, anti-expertise, anti-intellectual and anti-media,” said Whit Ayres, a Republican strategist, adding that Dr. Fauci “is an establishment expert intellectual who is in the media.”

For the 81-year-old immunologist, a venerated figure in the world of science, it is a jarring last chapter of a government career that has spanned half a century. As director of the National Institute of Allergy and Infectious Diseases, a post he has held since 1984, he has helped lead the response to various public health crises, including AIDS and Ebola, and advised eight presidents. He has never revealed a party affiliation. President George H.W. Bush once cited him as a hero.

Now, though, some voters are parroting right-wing commentators who compare Dr. Fauci to the brutal Nazi doctor Josef Mengele. Candidates in hotly contested Republican primaries like Ohio’s are trying to out-Trump one another by supplanting Speaker Nancy Pelosi with Dr. Fauci as a political boogeyman. Mr. DeSantis has coined a new term: “Faucism.” In Washington, lawmakers are taking aim at Dr. Fauci’s salary, finances and influence.

“I didn’t make myself a polarizing figure,” Dr. Fauci declared in an interview. “I’ve been demonized by people who are running away from the truth.”

The anti-Fauci fervor has taken its toll on his personal life; he has received death threats, his family has been harassed and his home in Washington is guarded by a security detail. His standing with the public has also suffered. In a recent NBC News Poll, just 40 percent of respondents said they trusted Dr. Fauci, down from 60 percent in April 2020.

Still, Mr. Ayres said, Dr. Fauci remains for many Americans “one of the most trusted voices regarding the pandemic.” In a Gallup poll at the end of 2021, his job approval rating was 52 percent. On a list of 10 officials, including Mr. Biden and congressional leaders, only two scored higher: Chief Justice John G. Roberts Jr. and Jerome H. Powell, the chairman of the Federal Reserve.

Republican strategists are split on whether attacking Dr. Fauci is a smart strategy. Mr. Ayres said it could help rev up the base in a primary but backfire in a general election, especially in a swing state like Ohio. But John Feehery, another strategist, said many pandemic-weary Americans viewed Dr. Fauci as “Mr. Lockdown,” and it made sense for Republicans “to run against both Fauci and lockdowns.”

Here in Ohio, Ms. Timken, a Harvard graduate and former chairwoman of the Ohio Republican Party who promises to “advance the Trump agenda without fear or hesitation,” is doing just that. Her ad shows a parent struggling to put a mask on a screaming toddler, which she brands “child abuse.”

The spot, she said in an interview, was prompted by what she hears from voters who are resentful of vaccine mandates, confused by shifting public health advice and tired of being told what to do.

“It taps into the real frustration they feel,” Ms. Timken said, “that Fauci claims to be the bastion of science, but I think he’s playing God.”

She is one of three candidates with elite academic credentials who are going after Dr. Fauci in a crowded primary for the seat that Senator Rob Portman, a Republican, is giving up. The others are J.D. Vance, a lawyer with a Yale degree and the author of the best-selling memoir “Hillbilly Elegy,” and Josh Mandel, the former Ohio state treasurer, whose law degree is from Case Western Reserve University.

Mr. Vance called Dr. Fauci “a ridiculous tyrant” during a rally with Representative Marjorie Taylor Greene, the far-right Republican banned from Twitter for spreading Covid misinformation. Mr. Mandel has railed against Dr. Fauci for months on Facebook and Twitter, calling him a liar and “one of the biggest frauds in American history.”

Ohio Republicans are split between the Trump wing and centrists in the mold of John Kasich, the former governor. Those tensions were on display last week at Tommy’s Diner, a Columbus institution, and at a meeting of the Franklin County Republican Committee, which convened to vote on endorsements. Sentiments seemed to track with vaccination status.

At the diner, Republicans like Mike Matthews, a retired state worker, and George Wolf, a retired firefighter, both of whom voted for Mr. Trump, found no fault with Dr. Fauci. Both are vaccinated. “I’ve never heard of anyone that I would trust more,” Mr. Wolf said.

But at the next table, Andy Watkinson, a remodeling contractor who is unvaccinated, said he was a fan of Joe Rogan, the podcaster, provocateur and Fauci critic. “I think he’s done the same thing for 50 years and he’s in bed with all the pharma companies,” Mr. Watkinson said of Dr. Fauci, though there is no evidence of that. “He needs to retire.”

At the committee meeting, views about Dr. Fauci were more strident.

“He needs to be brought up on charges,” declared Lisadiana Bates, a former business owner who is home-schooling her children. Echoing Dr. Robert Malone, who has become a conservative celebrity by arguing that Covid vaccine mandates are unethical experiments, she asserted that Dr. Fauci had “violated the Nuremberg Code,” the set of research ethics developed after the Holocaust.

“This whole thing is nothing but an experiment!” Ms. Bates exclaimed.

The roots of anti-Fauci campaign rhetoric can be traced to Washington, where Dr. Fauci has clashed repeatedly with two Republican senators who are also doctors: Mr. Paul, an ophthalmologist, and Senator Roger Marshall of Kansas, an obstetrician.

Mr. Paul has fueled speculation that Covid-19 was the result of a lab leak produced by federally funded “gain-of-function” research — high-risk studies aimed at making viruses more infectious — in Wuhan, China. Dr. Fauci and other National Institutes of Health officials have said that the Wuhan research did not meet the criteria for gain-of-function studies, and that it is genetically impossible for viruses studied there to have produced the pandemic.

The nuances of that dispute, however, have gotten lost in the increasingly hostile exchanges between the two men. In July, after Mr. Paul accused him of lying to Congress, Dr. Fauci shot back, “If anybody is lying here, senator, it is you.” Last month, Dr. Fauci arrived at a Senate hearing brandishing a fund-raising webpage for Mr. Paul that included a “Fire Dr. Fauci” graphic, and accused Mr. Paul of exploiting the pandemic for political gain.

Later in that same hearing, Dr. Fauci muttered under his breath that Mr. Marshall was “a moron” — a comment caught on an open microphone — after the senator posted Dr. Fauci’s salary on a placard and demanded his financial disclosure forms, suggesting he might be engaged in financial “shenanigans” with the pharmaceutical industry.

(Dr. Fauci’s financial disclosure forms, which Mr. Marshall has since posted on the internet, show investments in bonds and mutual funds, not drug companies. He is paid an annual salary of $434,312 under a provision that allows government doctors and scientists to be highly compensated, akin to what they could earn in the private sector.)

Dr. Fauci said he did not regret the “moron” remark, or the pushback against Mr. Paul. But Ms. Timken said calling Mr. Marshall a moron was “beyond the pale.”

Even some Fauci fans in academia and government say he might have been better off keeping his cool to avoid amplifying his Republican critics and alienating voters who need to hear his public health message. Some suggest he lower his profile; he says the White House asks him to go on TV.

“He’s been pushing back in a way that is not common for us to see for American scientists, and I don’t know if it’s a good idea,” said Dr. Ashish K. Jha, the dean of the Brown University School of Public Health.

If Democrats lose seats in the midterm elections, as many expect, Dr. Fauci may have a Republican-controlled Congress to contend with. Another Republican from Ohio, Representative Jim Jordan, who claims that Dr. Fauci knew the coronavirus “came from a lab,” has vowed that Republicans will investigate him if they win control of the House.

Some of Dr. Fauci’s friends are urging him to avoid that possibility by retiring. He has been working on a memoir, but cannot look for a publisher while he is still a federal employee. Dr. Fauci says Republicans will not dictate the terms of his retirement, and he has no plans at the moment to step down. And, he said, he is not worried about any investigation.

“I can’t think of what they would want to investigate except this whole pile of lies that they’re throwing around,” he said.