Dr. Dave Weldon, a former Republican congressman who is President-elect Donald J. Trump’s pick to lead the Centers for Disease Control and Prevention, has been off the political stage for more than 15 years.
Now running a private medical practice in Malabar, Fla., Mr. Weldon was hardly regarded as a leading candidate to run the federal agency, a $9 billion behemoth with a staff of more than 13,000 that has become a locus of conservative rage.
Yet over the years his views have aligned in many ways with those of Robert F. Kennedy Jr., Mr. Trump’s choice for health and human services secretary, and Dr. Weldon’s potential boss. The two have maintained a 25-year relationship.
Like Mr. Kennedy, Dr. Weldon, 71, has claimed that some children may develop autism when vaccinated against measles because of genetics or other factors, despite dozens of robust studies that thoroughly disproved the claim.
Reached by phone on Tuesday, he declined to say whether he still held those beliefs and added that he could not yet comment on “anything of substance.”
Dr. Weldon said that in his time in the House of Representatives, he worked with Mr. Kennedy “to get the mercury out of the childhood vaccines.” Still, he described himself as a supporter of vaccination.
Both his adult children are fully immunized, he said, and he prescribes thousands of doses of flu and other vaccines to his adult patients. “I’ve been described as anti-vaccine,” Dr. Weldon said, but “I give shots, I believe in vaccination.”
While in Congress, Dr. Weldon was sharply critical of officials at the C.D.C. and the Food and Drug Administration. They “failed to free themselves from conflicts of interest that serve to undermine public confidence in the safety of vaccines,” he said in 2007.
In that respect, Dr. Weldon’s views fit neatly with the agenda Mr. Trump and Mr. Kennedy have laid out to clean up what they believe to be corruption at the public health agencies. Mr. Kennedy has cited Dr. Weldon when airing his own criticisms of the C.D.C.
The two have echoed each other in other ways: “Is there some other underlying process going on to account for the larger and larger number of kids that are being labeled with these behavioral and learning disorders?” Dr. Weldon asked at a House committee meeting in 2002.
“And I’m specifically talking about something in the environment, something in the food that could be playing a role.”
Dr. Weldon served in Congress from 1995 to 2009 and was the first physician from Florida to be elected. He lost a primary bid for the Senate in 2012 and another for a seat in the Florida House just this year.
In 14 years in the House, he articulated some views that aligned with the scientific consensus and others that went against it. Dr. Weldon was studious, serious and soft-spoken, according to some people who worked with him.
But he frequently leveraged his credentials as a physician to support stances that cut against scientific consensus, particularly when religion tangled with science.
Dr. Weldon “has done some things, I think, has said some things that are appropriate, but also accepted some nonscientific things,” said Dr. Neal Halsey, professor emeritus at Johns Hopkins University who served as a scientific adviser to the C.D.C. during part of Dr. Weldon’s tenure in office.
Of the debunked notion that vaccines cause autism, Dr. Halsey said, “I don’t know why Weldon latched on to this and why he doesn’t change.”
Still, “he’s not the worst possible person who could be appointed to direct C.D.C.”
Dr. Weldon is perhaps best known for the Weldon Amendment, which bars health agencies from discriminating against hospitals or health insurance plans that choose not to provide or pay for abortions.
During the first Trump administration, health officials tried to put the amendment to broad use. They threatened to withhold $200 million in Medicaid funds from California, for example, on the grounds that the state required health plans to cover abortion.
“It infused into our health care system this very mushy language that the anti-abortion movement has weaponized,” said Leila Abolfazli, director of abortion strategy at the National Women’s Law Center.
While in Congress, Dr. Weldon also sought to restrict some types of abortions and promoted some dubious theories, including one about a link between abortion and breast cancer that was not supported by in-depth research.
He was a prominent voice in the early 2000s in the debate over Terri Schiavo, a Florida woman who had sustained a brain injury that left her in a persistent vegetative state.
Ms. Schiavo’s husband said she would not have wanted to be kept alive, but her parents and some lawmakers disagreed, including Dr. Weldon. Removing Ms. Schiavo’s feeding tube would be “a grave injustice,” Dr. Weldon told Congress in 2003.
(Two years later, after the tube was removed, an autopsy found that Ms. Schiavo’s brain had withered to half the normal size and that no treatment could have improved her condition.)
In 2001, Dr. Weldon sponsored a ban on human cloning and proposed criminal penalties for scientists, doctors and patients, including those who might seek related therapies abroad.
He also argued that abstinence was the most effective way to curb sexually transmitted infections.
But some of his other efforts did not fall cleanly along partisan lines.
In 2003, at President George W. Bush’s behest, Dr. Weldon was one of three Republicans to sponsor a bipartisan bill to provide $15 billion for H.I.V., tuberculosis and malaria programs in poor nations. The program, PEPFAR, is now credited with saving more than 25 million lives.
Dr. Weldon also teamed up with Lynn Rivers, Democrat of Michigan, on a bill to ban patents for gene-based diagnostic tests. Certain patents allowed companies to hold monopolies on these tests, keeping costs too high for many people.
He questioned the need to immunize children against hepatitis B, viewing it primarily as a sexually transmitted disease afflicting adults. He was far from alone, Dr. Halsey recalled.
Advisers to the C.D.C. had recommended vaccinating newborns because infected mothers were passing the virus to them, said Dr. Halsey, who was involved in that decision.
“There was a lot of difficulty that many physicians had with understanding the rationale,” he said. “We probably should have and could have done a better job at educating people before making the recommendation.”
In interviews, some experts noted that Dr. Weldon had no training or experience in public health and had not run an organization as big as the C.D.C.
But Dr. Weldon’s past views on autism worry public health experts and some Democratic lawmakers most.
“It doesn’t take much to disrupt the vaccination program,” said Dr. Joshua Sharfstein, a former F.D.A. official who is now a vice dean at Johns Hopkins.
In the early 2000s, Dan Burton, a Republican from Indiana who presided over the Committee on Government Reform, led a series of hearings on the risks of vaccines to children, prompted by his grandson’s autism diagnosis. Dr. Weldon was among the most prominent voices.
“He was one of the best people we had on the committee,” Mr. Burton recalled. “I can think of nobody that would do a better job” as C.D.C. director, he added.
The inquiries began after a British study of 12 children suggested that the measles vaccine might cause autism in some children.
Dr. Weldon appeared to be “very sincere” in his empathy for people who believed their children became autistic after vaccination, said Dr. Sharfstein, who worked then for Representative Henry Waxman, Democrat of California.
A member of the House Autism Caucus, Dr. Weldon invited Andrew Wakefield, who led the initial study and was later barred from practicing medicine in his native Britain, to a Congressional session on autism and childhood vaccines.
But as study after study in reputable medical journals found no association between vaccines and autism, Dr. Weldon remained unconvinced.
He criticized large epidemiological studies — which look at diseases at the level of populations — as too far removed from the clinic, and clinical studies, including those larger than the British one, as too small.
Dismissing epidemiology when leading an agency staffed by many epidemiologists is likely to create confusion within the C.D.C. and beyond, said Dr. Georges Benjamin, who heads the American Public Health Association.
“Epidemiology and statistics is the tool of science,” Dr. Benjamin said. “That is how we make sure it’s more likely to be true and not by chance, and if he doesn’t understand that or trust that — boy, that’s a problem.”
In 2004, the Institute of Medicine conducted a thorough review of available studies on autism and vaccines, and found insufficient evidence for a link. Dr. Weldon rejected those findings, too.
“C.D.C. needs a leader who can integrate all the evidence that exists,” Dr. Sharfstein said. “There’s every reason to be concerned if the Dave Weldon who becomes the C.D.C. director is the Dave Weldon of 20 years ago.”
On one issue, Dr. Weldon and some prominent experts on vaccine safety are aligned.
In Congress, Dr. Weldon pushed to move the vaccine safety office out of the C.D.C., and to re-establish it as an independent entity within the Health and Human Services Department. Dr. Weldon argued that the C.D.C. had a conflict of interest because it also purchased and promoted vaccines.
Other critics have made the same point. They have also noted that the budget for vaccine safety is $20 million, compared with the roughly $4 billion spent on purchasing and distributing vaccines.
“I’m not criticizing the efforts that C.D.C. makes in purchasing and promoting vaccines — it’s really important, it saves a lot of lives,” said Daniel Salmon, director of the Institute for Vaccine Safety at Johns Hopkins Bloomberg School of Public Health and lead author of the paper.
But “that’s just not who should be doing the vaccine safety assessment,” he added.
An independent vaccine safety agency akin to the National Transportation Security Board, with enough resources and subpoena power, could better assuage the public’s fears, Dr. Salmon said.
In 2017, Dr. Weldon became president of the Alliance of Health Care Sharing Ministries, an umbrella organization for faith-based groups offering alternatives to traditional health insurance.
The groups’s cost-sharing plans came under scrutiny from regulators for aggressive marketing tactics that led to widespread confusion about whether the plans were legally obligated to pay for medical claims.
Dr. Weldon stepped down as president in 2020 because he was “interested in slowing down,” he said.
“In the brief time I did that, I strongly encouraged all the ministries to get together and form an accreditation system, and I think they did,” he said on Tuesday.
But “I left, and I don’t know how rigorous it really was.”
Dr. Weldon grew up on Long Island, and he and his wife, Nancy, still return to New York City to see Broadway shows — which he enjoys and she does not.
At 71, Dr. Weldon said he is “just a kid” compared with Mr. Trump; he is just a few months older than Mr. Kennedy, who he likened to “the Energizer Bunny.”
His daughter lives in Atlanta, where the C.D.C. has its headquarters, and maintains a spare bedroom for her parents’ visits, he said. If confirmed as the agency’s director, he plans to stay with her when he starts at the agency.
