But while the ultimate fate of those actions is unknown, there is one area to which experts say Trump’s administration unquestionably has already done real damage: public health. And many of those who’ve spent their adult lives on the front lines, keeping Americans and the world safer from infectious diseases and other threats, believe that damage will be long-lasting.

“What concerns me the most is how difficult the rebuild is going to be once things finally turn around,” says Ursula Bauer, a former disease prevention executive at the federal Centers for Disease Control and Prevention (CDC). “The forced exodus of highly skilled, highly educated researchers, scientists and professionals from the federal government is really just extraordinary…It is going to take decades to rebuild.”

A national cross-section of workers in public health and medical research, along with some of those who’ve recently emerged through the professional pipeline, shared similar sentiments in interviews this week with Fortune. Together, they drew a grim picture of the short- and longer-term implications of the Trump administration’s severe cuts to federal health staffing and funding.

Spending reductions, they say, are already pausing critical research into how to prevent future pandemics, among many other areas. Amid one of the worst measles outbreaks in decades, the cuts in federal money mean fewer people working at the state and local level to contain it, almost assuring that the outbreak will grow. The wholesale dismantling of the CDC’s Office on Smoking and Health could undo decades of progress in reducing American death rates from tobacco-related lung cancer.

Lab specimens are sitting on shelves, experts say, because there no longer are enough federal workers to analyze them. A 20,000-person workforce shrinkage at the Department of Health and Human Services (HHS), meanwhile, includes a swath of the top experts and leaders in their fields, creating an organizational void with no stated plan for how to fill it.

An HHS spokesperson confirmed the 20,000 figure to Fortune on Thursday, stating that its reduction in force cut about 10,000 employees and another 10,000 retired or resigned. This represents nearly a 25% cut to the department’s workforce, from 82,000 to 62,000. HHS Secretary Robert F. Kennedy, though, has already noted that 20% of the 10,000 dismissals were made erroneously. “Personnel that should not have been cut, were cut. We’re reinstating them. And that was always the plan,” Kennedy said.

The spokesperson did not answer a series of questions, instead pointing to general comments made previously by Kennedy in which he said the department overhaul “is about realigning HHS with its core mission: to stop the chronic disease epidemic and make America healthy again. Despite spending $1.9 trillion in annual costs, Americans are getting sicker every year, and we must shift course.”

“They’re breaking lots of stuff without knowing what they’re breaking,” says Georges Benjamin, longtime executive director of the American Public Health Association, the largest organization of public health officials in the world. “This results in the loss of really critical infrastructure, demoralizing the workforce. And the part that they’re breaking is the part that gives you the best buy for your health.”

Trump’s and Kennedy’s assaults on federal research—and the government funding that helps pay for the work at revered U.S. research institutes and universities—are grounding critical projects mid-stream. The CDC recently pulled back more than $11 billion in grants to state and county health departments, money that was initially allocated during the peak of the COVID pandemic.

Local departments have used the funding to respond to other public health needs, including tracking diseases and providing treatment for addiction. A federal judge temporarily blocked the cuts after 23 states and the District of Columbia sued to prevent them, and Kennedy later told CBS News that he was unfamiliar with the cuts that had been made.

At the renowned biomedical research institution Rockefeller University in New York, “We were three years into a five-year project to study how to make better vaccines,” says Paul Bieniasz, a professor of retrovirology. The project began in response to COVID-19, but its ultimate aim is to make vaccines that will be effective against a broader array of coronaviruses.

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That project required administrative approval from the National Institutes of Health to continue its final two years, at a cost of about $2 million per year, Bieniasz says. Though such NIH approval is usually routine, it never came, and the virologist says he found out in a roundabout way that the funding had been cut. Bieniasz’s lab is appealing the termination of the grant, one of several under which it operates.

“In the medium to long term, the diminution of resources will drive people away from careers in science,” says Bieniasz, himself an immigrant who came to the U.S. to pursue his dream of becoming a scientist. (He recently wrote an op-ed on the topic for The Guardian.) “A large fraction of the people I hire to staff my lab are smart people from overseas who want to come here to be scientists. This of course will end if we continue on this path of throttling science.”

This, interview subjects repeatedly tell Fortune, is the true existential threat of Trump declaring open season on U.S. health systems, research institutes and universities. In the absence of funding to begin or continue crucial medical and scientific research, the pipeline of domestic and international talent will begin drying up—and it will occur at the exact moment that China is striving to become a biomedical and biopharmaceutical superpower.

“Maintaining our excellence is not going to be easy—trying to find paths to preserve our very important [research and development] infrastructure, which has been so successful ever since World War II,” says Peter Hotez. Hotez is an American scientist who co-led the development of a low-cost, no-patent COVID vaccine that has reached 100 million people.

“We’ve had 80 years of successes, and we started research universities,” Hotez says. “Institutions are America’s treasures, and I think that could likely erode. And what does this mean for young people who are looking at all this and saying, My God, what am I going to do in life? I mean, do I really want to embark on advanced scientific training if I can’t support a scientific career in the United States?”

That concern is on the minds of America’s scientists, 2,000 of whom co-signed a public letter in which they described a “climate of fear” among researchers. The letter declared that Trump’s administration “is blocking research on topics it finds objectionable, such as climate change, or that yields results it does not like, on topics ranging from vaccine safety to economic trends.”

“We are sending this SOS to sound a clear warning: The nation’s scientific enterprise is being decimated,” the letter says. “If our country’s research enterprise is dismantled, we will lose our scientific edge.”

Every health agency has been impacted, says Angela Rasmussen, a virologist at the University of Saskatchewan. “This restructuring is actually slashing the budget for research, and it will severely impair if not completely abrogate most of our national capacity to respond to health emergencies and carry out our basic public health functions,” Rasmussen says. “There are no positives to these cuts I can imagine.”

As Kennedy’s sudden backtracking on the HHS reductions suggests, it isn’t clear what the final tallies will be in terms of funding and staffing cutbacks. What is known is that the cuts will continue to run deep and, in either a few or many cases, will be motivated by almost any force besides the actual value of the work being done.

At Columbia University, PhD candidate Daniella Fodera learned in March that her NIH fellowship was being terminated. Fodera’s doctoral research focused on studying the biomechanics of human uterine fibroids, noncancerous tumors that can cause women severe pelvic pain, menstrual bleeding and infertility. But the termination had nothing to do with that; rather, Fodera says the note she received from the NIH said the reason was “unsafe antisemitic actions that suggest the institution lacks concern for the safety and well-being of Jewish students.”

“The true emergency, as I see it, is the politically-driven attacks on science as a way to suppress free speech,” Fodera tells Fortune. “Science itself should be an apolitical, objective pursuit that benefits all of humanity, regardless of one’s race, sex, nationality, religion or political party affiliation. I do not believe for a second that terminating my grant does anything to combat antisemitism, and I believe it was an excuse for the Trump administration to target higher education and exert control and power.”

Where do science and medicine go from here? Even those at the top of their fields aren’t sure. The Trump cuts have thrown the research community into a wild state of uncertainty. While there are court challenges underway to force restoration of funding in some areas, critical research projects mostly sit idle. Some public information health campaigns have gone dark, and the CDC, long understood as a critical hub of data and analysis for the American health system, still does not have a permanent director.

“The slashing of positions at CDC, at FDA–there’s nothing about it that seems like it is based on a strategic approach to maintaining and improving the health of people in America and around the world,” says Richard Besser, former acting director of the CDC, who since 2017 has served as president and CEO of the Robert Woods Johnson Foundation.

“One of the things that we know about public health, and one of the challenges about public health, is that when our system is working well, it’s pretty much invisible,” Besser says. “You’re not seeing the outbreaks of vaccine-preventable disease that could be occurring. You’re not seeing children in doctors’ offices showing up with lead poisoning. You’re not seeing children walking to school, being unable to breathe because their asthma is being triggered by poor air quality…It’s going to take time to really see the impact [of gutting those operations].”

In the meantime, the experts say, Americans and those around the world are likely to get sicker, suffer more chronic disease, and need more advanced medical care—all of it at tremendous cost. That may mean a payday for the corporate health industry, but as health policy, it’s an almost incomprehensible step backward.

“A weaker CDC means a sicker, less safe and less prosperous America,” says Tom Frieden, former director of that agency and current CEO of the health nonprofit Resolve to Save Lives. “It may work in the private sector to blow things up and build them back. It doesn’t work that way in the government. These are complex systems. Maybe they need to be drastically improved, but ending them isn’t a way of improving them—it’s a way of ending them.”