A refinery in New Mexico that the federal government has accused of some of the worst air pollution in the country.

A chemical plant in Louisiana being investigated for leaking gas from storage tanks.

Idaho ranchers accused of polluting wetlands.

Under President Biden, the Environmental Protection Agency took a tough approach on environmental enforcement by investigating companies for pollution, hazardous waste and other violations. The Trump administration, on the other hand, has said it wants to shift the E.P.A.’s mission from protecting the air, water and land to one that seeks to “lower the cost of buying a car, heating a home and running a business.”

As a result, the future of long-running investigations like these suddenly looks precarious. A new E.P.A. memo lays out the latest changes.

E.P.A. enforcement actions will no longer “shut down any stage of energy production,” the March 12 memo says, unless there’s an imminent health threat. It also curtails a drive started by President Biden to address the disproportionately high levels of pollution facing poor communities nationwide. “No consideration,” the memo says, “may be given to whether those affected by potential violations constitute minority or low-income populations.”

Those changes, said Lee Zeldin, the E.P.A. administrator, would “allow the agency to better focus on its core mission and powering the Great American Comeback.”

David Uhlmann, who led enforcement at the agency under the Biden administration, said the memo amounted to the agency announcing that “if companies, especially in the oil and gas sector, break the law, this E.P.A. does not intend to hold them accountable.”

That would “put communities across the United States in harm’s way,” he said, particularly poorer or minority areas that often suffer the worst pollution.

Molly Vaseliou, a spokesperson for the E.P.A., said she could not comment on ongoing investigations or cases. The Department of Justice, which has faced its own staff and budget cuts, declined to comment.

Conservatives have argued that E.P.A. regulations have hurt economic growth and investment. “Bold deregulatory action at E.P.A. will unleash American energy and reduce costs for American families,” said Grover Norquist, President of Americans for Tax Reform, the anti-tax organization, in a statement. “The government’s expensive web of overregulation is being unwoven.”

To be sure, enforcement cases brought by the Biden administration are still winding their way through courts. On Wednesday, the Japanese truck manufacturer Hino Motors pleaded guilty to submitting false emissions-testing data in violation of the Clean Air Act and agreed to pay more than $1.6 billion in fines stemming from a probe first opened by California in 2019.

At the same time, a wider reframing of the purpose of the E.P.A. is underway. The agency was created a half-century ago, during the Republican presidential administration of Richard M. Nixon, with a mandate to protect the environment and public health.

Last week, the Trump administration said it would repeal dozens of the nation’s most significant environmental regulations, including limits on pollution from tailpipes and smokestacks, and protections for wetlands.

In a video posted to X, the social media site, Mr. Zeldin said his agency’s mission was now to “lower the cost of buying a car, heating a home and running a business.”

Project 2025, a blueprint for overhauling the federal government that was produced by the Heritage Foundation and written by many who are serving in the Trump administration, goes further, seeking to eliminate the E.P.A. office that carries out enforcement and compliance work. Mr. Zeldin has also said he intends to cut the agency’s spending by 65 percent and eliminate its scientific research arm.

Some on-site inspections, which form a vital part of enforcement investigations, are already being delayed or suspended, according to two people who spoke on condition of anonymity because they are unauthorized to speak publicly. Investigations related to air pollution were particularly vulnerable, they said.

There has already been one significant reversal. This month the Trump administration dropped a federal lawsuit against Denka Performance Elastomer, a chemical manufacturer accused of releasing high levels of a likely carcinogen from its Louisiana plant.

The Biden administration filed the lawsuit after regulators determined that emissions of chloroprene, used to make synthetic rubber, were contributing to health concerns in a region along the Mississippi River with some of the highest cancer risk in the United States.

“I honestly wonder if the malefactors are going to give us more burning rivers,” said William K. Reilly, E.P.A. administrator under President George H.W. Bush, speaking to reporters this month. He was referring to a fire on the polluted Cuyahoga River in Ohio in the late 1960s that helped galvanize environmental awareness.

And while the E.P.A. said it remained committed to addressing imminent health threats, the risks from pollution tend to play out over longer periods of time, in the form of increased rates of cancer, birth defects or long-term respiratory and cardiac harm, said Ann E. Carlson, a professor of environmental law at the UCLA School of Law.

“The memorandum is essentially a wink, wink to coal and oil interests that they can pollute with what may be close to impunity,” she said.

That would be a stark reversal after the Biden administration had worked to build up the agency’s enforcement work. In 2024, the E.P.A. concluded 1,851 civil cases and collected $1.7 billion in administrative and judicial penalties, both the highest levels since 2017. That same year, 121 criminal defendants were charged.

The agency had also prioritized policing greenhouse gas emissions, toxic “forever chemicals” known as PFAS, as well as the disposal of coal ash, the toxic material left over from burning coal.

The new Trump E.P.A. will pull back both from a focus on coal ash disposal, and from emissions of methane, a potent greenhouse gas, from oil and gas facilities, the recent memo said.

Other Biden-era enforcement settlements are waiting to be finalized, including one involving the decades-old HF Sinclair refinery in Artesia, N.M., accused of causing some of the worst concentrations of cancer-causing benzene in the country.

The E.P.A., together with the Department of Justice and the state of New Mexico, proposed a $35 million settlement in the final days of the Biden administration as part of an effort to protect people living in Artesia, a city of 13,000 people with a long history of pollution. HF Sinclair, which processes about 100,000 barrels of crude oil a day in Artesia, was also required to invest in fixes at the refinery that would reduce emissions of hazardous air pollutants.

So far, the Trump administration has not moved to finalize that settlement.

In a statement, the Texas-based operator said it had already invested in fixes and monitoring to address the allegations.

The New Mexico Department of Environmental Quality said it supported moving forward with the settlement “as expeditiously as possible,” adding that, “due to the change in administration at the federal level, timing is unclear.”

Investigations just getting started face even greater uncertainties, because the agency has leeway not to follow up on violations.

In March 2023, E.P.A. officials discovered leaks and other alleged violations of pollution laws during an inspection at a refinery and chemicals plant operated in Norco, La., by Shell, the Dutch oil and gas giant.

According to a notice later issued by the E.P.A., and obtained by the Environmental Integrity Project, a watchdog group, one chemical storage tank was found with “severe pitting across the entire fixed roof, as well as cracks/openings with detectable emissions.”

The E.P.A. has declined to say whether investigations were continuing. Shell declined to comment.

Some cases may be shaped by wider changes.

In 2021, E.P.A. inspectors found signs that a cattle ranch in Bruneau, Idaho, had disrupted protected wetlands by constructing road crossings and by mining sand and gravel from a local river. The agency sued, alleging violations of the Clean Water Act, in particular a bitterly contested rule adopted by the Obama administration known as “waters of the United States,” which extended existing federal protections to smaller bodies of water such as rivers, waterways and wetlands.

A federal judge dismissed the original case after a 2023 Supreme Court ruling curtailed the federal government’s authority to regulate smaller bodies of water. President Biden’s E.P.A. filed an amended lawsuit in September.

Last week, the E.P.A. said it would rewrite the rule to lower permitting costs for developers.

Ivan London, an attorney with the Mountain States Legal Foundation who is helping to defend the ranchers in the case, said that he expected his clients’ arguments to prevail regardless of the E.P.A.’s new rule-making. The ranchers argue that the E.P.A. has no authority to regulate the wetlands in question.

Still, the current Trump administration would certainly side more with the defendants, and that could affect the case, he said. “I’ve been surprised before, and I’m sure I’ll be surprised again,” he said.

Joan Presky worries about dementia. Her mother lived with Alzheimer’s disease for 14 years, the last seven in a memory-care residence, and her maternal grandfather developed dementia, too.

“I’m 100 percent convinced that this is in my future,” said Ms. Presky, 70, a retired attorney in Thornton, Colo.

Last year, she spent almost a full day with a neuropsychologist, undergoing an extensive evaluation. The results indicated that her short-term memory was fine — which she found “shocking and comforting” — and that she tested average or above in every cognitive category but one.

She’s not reassured. “I saw what Alzheimer’s was like,” she said of her mother’s long decline. “The memory of what she went through is profound for me.”

The prospect of dementia, which encompasses Alzheimer’s disease and a number of other cognitive disorders, so frightens Americans that a recent study projecting steep increases in cases over the next three decades drew enormous public attention.

The researchers’ findings, published in January in Nature Medicine, even showed up as a joke on the Weekend Update segment of “Saturday Night Live.”

“Dementia is a devastating condition, and it’s very much related to the oldest ages,” said Dr. Josef Coresh, director of the Optimal Aging Institute at NYU Langone Health and the senior author of the study. “The globe is getting older.”

Now the findings are being challenged by other dementia researchers who say that while increases are coming, they will be far smaller than Dr. Coresh and his co-authors predicted.

Using data from about 15,000 Americans over age 55, collected at four research clinics around the country from 1987 through 2020, Dr. Coresh’s team projected a lifetime dementia risk much higher than previous studies had: 42 percent, though most of that risk didn’t emerge until after age 85.

The higher lifetime number probably reflected the study’s reliance on a more diverse sample than earlier researchers had used, Dr. Coresh said, and more dementia cases identified through in-depth questionnaires, regular phone calls, medical records and death certificates.

The researchers applied their risk calculations to the U.S. population and estimated that the number of people who would develop dementia each year would roughly double, to about a million by 2060, from 514,000 in 2020.

Eric Stallard, an actuary and co-director of the Biodemography of Aging Research Unit at Duke University, read the study and thought the team “seemed very competent at their analysis” of individual risk.

But when it came to the projection that cases would double, which assumed that the incidence of dementia would remain stable over the next 40 years, “I don’t believe it,” Mr. Stallard said.

“The notion that the number of people with dementia will double over the next 25, 30 or 35 years due to the aging of baby boomers is widespread, it’s pervasive — and it’s wrong,” he added.

He and two other Duke researchers recently published a commentary in JAMA pointing out that the age-specific prevalence of dementia in this country had steadily declined for 40 years.

“If your risks are lower than your parents’ risks and this trend continues, you won’t see the doubling or tripling of dementia that’s been projected,” said Dr. Murali Doraiswamy, director of the Neurocognitive Disorders Program at Duke and a co-author of the JAMA article.

To be clear, experts agree that the number of people with dementia will climb in coming decades, simply because the disorder rises so steeply with age and the number of older adults in the United States will increase.

But Mr. Stallard estimates that the increase will be more like 10 to 25 percent by 2050. “It will still be a significant challenge for the health system in the U.S.,” he said.

The Duke group relied on its own long-term study of people over age 65, with more than 21,000 respondents in 1984 and about 16,000 in 2004, plus later data from the national Health and Retirement Study and the National Health and Aging Trends Study.

Their analysis found that among 85- to 89-year-olds, for instance, the proportion with dementia was about 23 percent in the cohort born in 1905. In those born 10 years later, the figure had dropped to about 18 percent.

By the time Americans born in 1935 reached their late 80s, about 11 percent had dementia; the projection for those born from 1945 to 1949 is now about 8 percent.

To Dr. Coresh, whose primary interest was in individual risk, the assumption that past declines would continue at about the current rate “would be great, but is quite an optimistic, dramatic decrease,” he said in an email.

Yet in another longitudinal study of older adults in England and China, published in Nature Aging last year, “we also found these quite marked improvements in more recently born cohorts,” said the lead author, Dr. John Beard, a medical epidemiologist at the Mailman School of Public Health at Columbia University.

“You would expect the increase in the absolute numbers of people with dementia in the U.S. will be less than we feared,” Dr. Beard said.

What has led to the decrease in dementia, also seen in several European countries? Often cited explanations include rising education levels, reduced smoking and improved treatment for high blood pressure and high cholesterol.

The Lancet Commission on dementia, intervention and care has developed a list of 14 modifiable risk factors, including greater use of hearing aids and reduced air pollution, that could still lead to greater declines.

Yet the reverse could also happen. If earlier and more widespread testing increases the number of dementia diagnoses, or if the definition of dementia broadens, rates will increase, Dr. Doraiswamy noted. Increasing life expectancy would have the same effect.

Obesity and diabetes, more common in recent decades, could lead to more dementia, but much-touted new drugs that reduce them could blunt that trend — if people can get them.

“None of this is inevitable,” said Dr. Gill Livingston, a psychiatrist at University College London who leads the Lancet Commission. “It depends on what we do.”

Public health policy makes a major difference, she noted, and, “The U.S. is in a time where policy is changing enormously.”

Dementia rates might rise, for example, “if people have less access to health care, so they are less likely to get their blood pressure treated and their high cholesterol treated,” Dr. Livingston said.

Slashed Medicaid coverage could lead to that result. So could a rollback of environmental policies, “if air pollution increases because of fossil fuels,” she added.

Already, dementia afflicts some American populations far more than others, researchers point out. Older women and Black people face greater risk, along with those who carry the APOE4 gene associated with Alzheimer’s disease.

Health disparities could mean that “affluent people will see lower rates of dementia” because of the new diabetes and obesity drugs, Dr. Doraiswamy said. “People who can’t afford them and whose conditions are not well-managed will see rates go up.”

The debate about how many older adults will develop dementia in coming decades, and about how individuals, families, government and the health care system should respond, will likely continue.

So will Ms. Presky’s fears.

For now, she enrolls in lifelong learning classes, takes walks and yoga classes despite orthopedic problems, listens to podcasts and reads a lot of history and fiction. She and her husband take in theater in New York and Phish concerts on the West Coast and will soon be heading to London and Paris.

Still, her advance directive contains many provisions about dementia. “I remain pessimistic,” she said, noting that her mother was diagnosed at 77. “I have seven more years before I meet her fate.”

NASA made a bet a few years ago that commercial companies could take scientific experiments to the moon on a lower budget than the agency could.

Last year, that was a bad bet. The first NASA-financed spacecraft missed the moon entirely. The second landed but fell over.

But this month, a robotic lander named Blue Ghost, built by Firefly Aerospace of Cedar Park, Texas, succeeded from start to finish.

On March 16, the mood at Firefly’s mission operations outside Austin was a mix of happy and melancholic. There was nothing more to worry about, nothing left to do — except watch the company’s spacecraft die.

A quarter-million miles away, the sun had already set on Mare Crisium, the lunar lava plain where Blue Ghost had collected scientific observations for two weeks.

For the solar-powered spacecraft, the hours remaining were numbered and few.

“I think the mood generally is pretty light,” Ray Allensworth, the spacecraft program director at Firefly, said that afternoon. “I think people are just excited and also just kind of relieved to see how well the mission went and just kind of taking a moment to enjoy the last few hours with the lander.”

Scientists with cargo on the other commercial moon missions had invested years of effort and ended up with little or nothing. Those NASA assigned to Blue Ghost are coming away with a cornucopia of new data to work with.

Robert Grimm, a scientist at the Southwest Research Institute in Boulder, Colo., who led one of the scientific payloads, acknowledged his good fortune. “Better than being a crater,” he said.

One of the NASA experiments had collected data just as Blue Ghost landed. Four cameras captured views from different angles of the exhaust of the spacecraft’s thrusters as they kicked up lunar dust and carved a small crater.

“This gives us the ability with these cameras to measure three-dimensional shapes,” said Paul Danehy, one of the scientists working on the project known as Stereo Cameras for Lunar Plume-Surface Studies, or SCALPSS.

Engineers want to understand those dynamics to prevent potential disasters when bigger and heavier spacecraft like SpaceX’s Starship land astronauts on the moon. If NASA sets up a lunar outpost, spacecraft will return to that site more than once. Rocks flying upward could knock out an engine on a descending spacecraft or damage nearby structures.

In early looks at the photographs, one of the surprises is that the exhaust plume from the thrusters started kicking lunar dust when Blue Ghost was still about 50 feet above the surface, higher than expected. The same camera system is to record the dust cloud from a much larger lander, the Blue Moon Mark 1, which Blue Origin, Jeff Bezos’ rocket company, plans to send to the moon later this year.

NASA not only wants to understand lunar dust, or regolith, but also how to get rid of it. The particles can be sharp and abrasive like shards of glass, posing a hazard to machinery and astronauts. An experiment on Blue Ghost called the Electrodynamic Dust Shield used electric fields to clean dust off surfaces.

Two experiments collected information that should cast light on the moon’s interior.

Dr. Grimm’s payload was the Lunar Magnetotelluric Sounder, the first of its kind deployed on the surface of another world.

To deploy, spring-loaded launchers flung four probes about the size of soup cans in four different directions. Connected by cables to the lander, the probes worked like supersized voltmeters. A second component, raised atop an eight-foot-high mast, measured magnetic fields.

Together, these readings reveal naturally occurring variations in electric and magnetic fields that tell how easily electric currents flow deep underground, and that tells something about what is down there. The conductivity of colder rocks, for example, is lower.

Blue Ghost also deployed a pneumatic drill, using bursts of nitrogen gas to excavate dirt. A needle at the end of the instrument measured temperature and how easily heat flows through the material. Because of rocks in the way, the drill went down only about three feet, not the 10 feet that had been hoped.

In videos, “you can see the rocks flying out and sparks,” said Kris Zacny, vice president of exploration systems at Honeybee Robotics, which built the drill.

Still, three feet was deep enough for the scientific measurements, Dr. Zacny said. Data from the drill and the magnetotelluric sounder could both give hints about how the moon and other rocky worlds formed or why the near side of the moon looks so different from the far side.

“It’s really a basic question about lunar geology we’re trying to answer,” Dr. Grimm said.

Honeybee, which is part of Blue Origin, also built a second device called PlanetVac to demonstrate a simplified technology to collect samples. This device used compressed gas to stir up regolith into a small tornado and direct it into a container.

The technology will be used on a robotic Japanese space mission known as Martian Moons Exploration, which will bring back samples from Phobos, a moon of Mars.

“The fact that it worked on the moon gives us confidence that it should work on Phobos as well,” Dr. Zacny said.

Brian Walsh’s experiment on Blue Ghost did not look at the moon but back at Earth.

“It’s a really good vantage point,” said Dr. Walsh, a professor of mechanical engineering at Boston University.

Dr. Walsh is interested in the magnetic bubble that deflects solar wind particles around Earth. His telescope recorded X-rays emitted when high-speed particles from the sun slam into atoms in Earth’s upper atmosphere. The boundary between the Earth’s magnetic field and the solar wind is like two sumo wrestlers pushing against each other. The view from afar should help scientists tell whether that boundary shifts slowly or in sudden leaps.

That is important because it affects how well Earth’s magnetic field protects us from occasional gargantuan belches of charged particles that bombard the planet during solar storms.

“We’re trying to figure out how that gate opens and how energy spills through,” Dr. Walsh said.

Blue Ghost has already left a lasting impression.

Maria Banks said that as she left the mission operations center each night, she would look up at the moon hanging in the sky.

“Which would just basically stop me in my tracks every day,” Dr. Banks said. “I don’t think I’ll ever see the moon the same again, because for the rest of my life, Firefly’s lander and our instruments will be up there.”