The leader of the Republican Party and our country’s next president has tapped a pro-choice scion of the country’s most famous Democratic dynasty to lead the Department of Health and Human Services. In keeping with the bewildering dynamics of today’s negative partisanship, conservative groups such as the Heritage Foundation have cheered the selection of Robert F. Kennedy Jr., while liberals have near categorically denounced him.

Mr. Kennedy’s transformation from left-wing vaccine skeptic to potential Republican cabinet member overseeing America’s vast health apparatus represents a profound shift not only in the character of the American right but also in the politics of science more generally. The emergent MAGA science policy agenda, driven by skepticism and anti-elitism, blends familiar conservative and libertarian ideas with a suspicion of expert power once more associated with the left. The result is a uniquely American brand of populism that has the potential to fundamentally reshape national politics.

In retrospect, the science policy of Donald Trump’s first administration was remarkably conventional, at least until Covid struck. He filled many science policy posts with figures highly regarded in the scientific community, even retaining Francis Collins as director of the National Institutes of Health.

There were controversies surrounding environmental policy, including the administration’s decision to withdraw from the Paris climate accord. But those were familiar Republican fare, reminiscent of disputes during the Reagan and Bush eras. When it came to health agencies, many of Mr. Trump’s picks — Scott Gottlieb for commissioner of the Food and Drug Administration and Alex Azar for secretary of health and human services — had impeccable reputations in the Republican establishment. The criticism from the left was mostly the tired refrain that they were too cozy with the pharmaceutical industry.

Yet Mr. Trump left office amid a virulent backlash against scientific and medical expertise, marked by sharp declines in public trust, especially among Republicans. The administration that began Operation Warp Speed to develop vaccines to defeat the worst pandemic in a century ended in an epidemic of vaccine skepticism.

While most Americans still support the benefits of vaccination, Republicans today tend to be more vaccine hesitant than Democrats and more distrustful of the pharmaceutical industry generally. Compared with Democrats, Republicans are more likely to believe that the Food and Drug Administration is preventing natural cures from reaching the public because of corporate influence and that genetically modified organisms threaten public health. In short, Republican attitudes toward the scientific and medical establishment increasingly resemble the worldview embodied by Mr. Kennedy.

Far from being an eccentric one-off cabinet pick, then, the choice of Mr. Kennedy for a role in the new administration reflects the discontents, distrust and even paranoia of many within the current G.O.P. Mr. Trump’s first administration now looks like a hinge moment, a point of transition between two political paradigms.

The last time the politics of science underwent a similarly striking shift was in the second half of the 20th century. The federal scientific establishment in its modern form dates to the decades after World War II. Inspired by the mobilization of science during the war (exemplified by the Manhattan Project) and further catalyzed by geopolitical competition (including the Soviet launch of Sputnik in 1957), Congress created or expanded a range of science agencies, from the N.I.H. to the National Science Foundation to the National Aeronautics and Space Administration.

But by the late 1960s, the techno-optimism of the postwar years was losing steam. The Vietnam War, the politics of nuclear technology and the nascent environmental movement fueled a backlash against the alliance of science and the state. Student activists protested the co-optation of science by the so-called military-industrial complex. After the economic crisis of the 1970s, the wider public began to lose confidence that lavishly funded scientific institutions could deliver on their promises. By the end of the decade, the private sector overtook the public sector as the nation’s principal source of research funding.

Yet the state remained pivotal in shaping America’s scientific enterprise, sparking new tensions. Republicans decried the innovation-stifling effects of federal regulations, and Democrats worried about the societal and environmental impacts of unchecked technological development. Amid this push and pull, federal funding of basic science — especially biomedical research — came to occupy the uncontroversial political center. And after briefly stalling in the early 1980s, this funding grew continually, culminating in the doubling of the N.I.H.’s budget over five years around the turn of the millennium.

Some historians have identified the Great Recession as marking the end of a neoliberal political order that had predominated since the late 1970s. Historians may come to view the Covid-19 pandemic as marking a similar turning point in the politics of science. And Mr. Trump’s nomination of Mr. Kennedy may signal what comes next.

Mr. Kennedy has migrated across the political spectrum, but he represents a stance that diverges sharply from that of the old G.O.P. If the center-right view of health policy used to be that the F.D.A. was too cautious, stifling private-sector innovation, his “Make America Healthy Again” plan aims “to dismantle the corporate stranglehold on our government agencies that has led to widespread chronic disease, environmental degradation and rampant public distrust.” This language is closer to the leftism of Ralph Nader than to the market-friendly posture of the Chamber of Commerce.

Meanwhile, the onetime bipartisan consensus on biomedical research can no longer be taken for granted, with Republicans on Capitol Hill now poised to tighten the reins on the N.I.H. If Mr. Kennedy succeeds Xavier Becerra as health and human services secretary, N.I.H. overhaul will probably be a major focus of the new administration. The naming of Covid lockdown critic Dr. Jay Bhattacharya as a potential N.I.H. director suggests as much.

One might be tempted to interpret Republicans’ shifting stance on the N.I.H. as an expression of conventional small-government conservatism. But it is better understood as an expression of the right’s push for greater oversight of health agencies since the Covid-19 pandemic. Tellingly, the former House speaker Newt Gingrich — who spearheaded the G.O.P.’s rise to power in the 1990s and oversaw the doubling of the N.I.H. budget — has come out in favor of congressional Republicans’ proposed cuts to the agency, citing the pandemic as the reason for his volte-face.

To be sure, the MAGA approach to science echoes some traditional Republican concerns. Right-wing disdain for intellectual elites is hardly new. Social conservatives have long expressed unease about appeals to scientific authority that ignore moral and religious values. And fiscal conservatives and libertarians have always resisted the unchecked growth of federal bureaucracies.

But the MAGA science policy agenda represents something novel in our national politics, blending discontents from the right and the left. It remains, at this stage, more a bundle of instincts than a coherent agenda, reflecting a coalition of forces marked by internal tensions and even contradictions.

If there’s a thread tying this coalition together, it’s a suspicion that expert authority hides elite power. This points to a future of science shaped by clashes between the establishment and its challengers. The distrust driving this new politics of science is a response to the technocratic hubris and at times gross incompetence that have too often characterized America’s institutions in recent years. Were this animus channeled into constructive policies and reforms, it could offer a needed corrective. In its unvarnished form, however, it is more radical than conservative, more destructive than constructive and more corrosive than restorative.

If this is what winds up driving the science policy agenda of the second Trump administration, then the prescriptions that follow will almost surely be worse than the diseases they are meant to cure. Yet any alternative that dismisses rather than speaks to the concerns that have driven so many Americans away from the expert establishment and toward a figure such as Mr. Kennedy will surely fail.