More than four years ago, former President Donald Trump’s administration accelerated the development and rollout of the covid-19 vaccine. The project, dubbed Operation Warp Speed, likely saved millions of lives. But a substantial number of Republican voters now identify as vaccine skeptics — and Trump rarely mentions what’s considered one of the great public health accomplishments in recent memory.

“The Republicans don’t want to claim it,” Trump told an interviewer in late September.

Instead, on at least 17 occasions this year, Trump has promised to cut funding to schools that mandate vaccines. Campaign spokespeople have previously said that pledge would apply only to schools with covid mandates. But speeches reviewed by KFF Health News included no such distinction — raising the possibility Trump would also target vaccination rules for common, potentially lethal childhood diseases like polio and measles.

The Trump campaign did not respond to requests for comment on this article.

Trump has presided over a landslide shift in his party’s views on vaccines, reflected this campaign season in false claims by Republican candidates during the primaries and puzzling conspiracies from prominent conservative voices. Republicans increasingly express worry about the risks of vaccines. A September 2023 poll from Politico and Morning Consult showed a narrow majority of those voters cared more about the risks than the benefits of getting inoculated.

A surge in anti-vaccine policy in statehouses has followed the rhetoric. Boston University political scientist Matt Motta, who tracks public health policy, said preliminary data shows that states enacted at least 42 anti-vaccine bills in 2023 — nearly a ninefold surge since 2019.

In some states, it has the look of a crusade: The 2024 Texas GOP platform, for example, proposes a ban on mRNA technology, the innovation behind some covid-19 vaccines that scientists believe could have significant applications for cancer care.

Last month, Trump made an appeal to anti-vaccine voters by landing the endorsement of Robert F. Kennedy Jr., one of the nation’s most prominent vaccine skeptics — and appointing him to his transition team. In a recent tour with former Fox News broadcaster Tucker Carlson, Kennedy said he was “going to be deeply involved in helping to choose the people who run FDA, NIH, and CDC.”

Trump’s outreach can be more discreet: He recently met with a delegation of vaccine-skeptical activists — including one group pushing an end to mandates and certain types of vaccines — at his New Jersey golf club; the discussion was publicized by the conservative blog “Gateway Pundit.”

Trump has options in advancing anti-vaccine goals as president, such as by sowing further doubt and undermining the federal government’s ability to make vaccine recommendations. He has promised to appoint Kennedy, along with “top experts,” to a panel exploring chronic diseases, some of which Kennedy’s nonprofit has linked to inoculations. “Nobody’s done more” to advocate for “the health of our families and our children,” Trump declared at a rally accepting Kennedy’s endorsement.

Still, it’s hard to tell how Trump’s most frequently made proposal — defunding schools that mandate vaccinations — would translate into action, said Judith Winston, former general counsel of the Department of Education during the Obama administration.

Currently, the Department of Education lacks the power to turn off public school funding all at once, she said — meaning a second Trump administration would have to take away money program by program.

And the legal basis for such a move isn’t clear. “I am unaware of any federal law that mandates school districts either provide or not provide a vaccine,” Winston said, adding it would probably require congressional action.

All 50 states have a vaccine requirement tied to school attendance.

Trump’s outreach to anti-vaccine constituencies comes as vaccine hesitancy increases and preventable disease surges. This summer, Oregon experienced its worst outbreak of measles since 1991.

The situation could get worse, said Tom Frieden, a former director of the Centers for Disease Control and Prevention: In the Nineties, during a time when vaccine skepticism also proliferated, the U.S. saw thousands of measles cases. According to the CDC, we haven’t yet returned to those bad old days — but the number of measles cases recorded this year is already quadruple that of last year.

“It was highly disruptive,” he said. “Many children who had measles ended up with hearing problems or cognitive problems that were lifelong. A small number died in this country.”

Worldwide, the disease killed over 100,000 in 2022, mostly among children under age 5, according to the World Health Organization.

Polling shows a substantial minority of Americans, concentrated in the Republican Party, hold vaccine-skeptical positions, said Harvard professor and health politics expert Robert Blendon.

And skepticism about covid vaccines is blossoming into suspicion of vaccines generally among that group, he said. “It follows from this rebellion against the covid vaccine mandates.”

Vaccine opposition has divided the GOP. Florida Gov. Ron DeSantis made opposition to vaccines a core part of his ill-fated campaign for the GOP presidential nomination. In states such as Wyoming and Missouri, pitched primary campaigns centered on anti-vaccine themes this year.

Bob Onder, a physician and Republican candidate for Congress in Missouri, was accused in Facebook ads placed by his top opponent of taking millions from pharmaceutical companies to test vaccines. “He profited from our pain,” one ad said. “You suffered the consequences.”

Onder “has never done covid vaccine research” and opposes covid vaccine mandates, his campaign manager, Charley Lovett, told KFF Health News. (Lovett said Onder “conducted” one study sponsored by AstraZeneca on preventing covid in high-risk patients using monoclonal antibodies, not vaccines.)

Onder won the Republican primary, but his vaccine-disparaging opponent still scored just over 37% of the vote.

Anti-vaccine candidates typically become anti-vaccine policymakers. The impact can be seen in Texas, where vaccine politics were once a bipartisan matter. According to researchers, from 2009 to 2019, legislators there passed 19 pro-vaccine bills, such as a measure allowing pharmacists to administer immunizations.

But that consensus began to shift toward the end of the decade. Small groups, often nurtured on Facebook, made their influence felt. One such group, Texans for Vaccine Choice, spurred testimony before the state legislature in 2021 and targeted pro-immunization legislators, some of whom fell in their GOP primaries.

Misinformation has fueled the anti-vaccine turn in Texas, alongside traditional conservative attitudes about individual autonomy, said Summer Wise, a former executive committee member of the state’s Republican Party — particularly misconceptions about the use of fetal cells in vaccine development; falsified research about a link between vaccines and autism; and conspiracy theories about Bill Gates, the billionaire philanthropist who has championed vaccination.

“Politicians see vaccines as an easy foil to propagate fear among the electorate, which can then be leveraged and directed to control a voting bloc,” Wise said.

In addition to calling for a ban on mRNA technology, the Texas GOP’s 2024 platform features a laundry list of policies that could undermine vaccination, including allowing medical residents and physicians the ability to opt out of administering shots for religious reasons. It also calls for enshrining a patient’s ability to opt out of vaccine mandates in the state’s Bill of Rights.

Nationally, anti-immunization policies could take an aggressive turn under a second Trump administration.

Roger Severino, formerly head of the Department of Health and Human Services’ Office of Civil Rights and now with the Heritage Foundation, penned the health agency section of Project 2025, the Heritage Foundation-led initiative to plan for a Republican administration.

Among other ideas, the document proposes clipping CDC authority to issue vaccine or quarantine guidance of a “prescriptive” nature, targeted at schools or elsewhere.

A spokesperson for the Heritage Foundation noted Severino has said the agency’s credibility has been hurt, and it has a burden to explain “all the vaccines on the schedule being taken in combination.”

The proposal misunderstands CDC’s history and powers, said Lawrence Gostin, a public health law professor at Georgetown University. The agency “rarely if ever” makes binding recommendations, he said.

“When the next pandemic hits, we will look to CDC to offer guidance based on the best-known evidence,” he said. “We don’t want a disempowered agency in a public health emergency.”

Some Republican intellectuals have spun dystopian visions surrounding vaccines. Take “Dawn’s Early Light,” a yet-to-be-published book by Heritage president Kevin Roberts. The tome — which earned a glowing foreword by Republican vice presidential nominee JD Vance — reserves especially sharp words for vaccines.

In one section of the book, Roberts imagines that the federal government would somehow use alleged new capabilities to “deplatform drivers” of cars for “failing to follow the latest vaccine mandate.”

“Yet another powerful tool of social control falls into place,” he wrote.