Over the course of 20 days in March 2020, 55 million American children stopped going to school as Covid-19 swept the United States.

What was impossible to anticipate then was that millions of those students would not return to classrooms full-time until September 2021, a year and a half later.

Those children and teenagers, often in public schools in Democratic areas, remained online at home while private schools, child-care centers, public schools in conservative regions, office buildings, bars, restaurants, sports arenas and theaters sputtered back toward normalcy.

Five years on, the devastating impact of the pandemic on children and adolescents is widely acknowledged across the political spectrum. School closures were not the only reason the pandemic was hard on children, but research shows that the longer schools stayed closed, the farther behind students fell.

What would happen if another health crisis came along — a pressing concern, as cases of measles and bird flu emerge? In the face of a new unknown pathogen, how would school leaders and lawmakers make decisions?

“It’s so important for Democrats to do a retrospective on this episode,” said Representative Jake Auchincloss, Democrat of Massachusetts, who represents a district in the Boston suburbs where some schools were fully or partially closed for a year. He has argued that during the pandemic, his party “over-indexed” toward the views of teachers’ unions and epidemiologists, who often pushed for a slow, cautious approach to reopening schools.

The extended closures “crystallized how the party has been failing in governance,” Mr. Auchincloss said.

In some ways, moving to online learning would be easier next time, now that nearly all schools give students their own laptops or tablets. And in places where schools remained closed longer, some people in positions of power, including health officials and leaders of local teachers’ unions, say they stand by the decisions they made at the time.

Still, in interviews with more than a dozen leaders in health, education and politics, including some who were key figures at the time, others said they would take a different approach in the future, and try to do more to avoid extended shutdowns for entire school districts.

“Yes, I’ve learned a lot from this,” said Randi Weingarten, president of the American Federation of Teachers and a powerful force in Democratic politics who at times worked behind-the-scenes to negotiate reopenings. She also stood by locals in places like Philadelphia and Chicago, where union members fought for vaccines, tests, ventilation and other safety measures — even after classrooms in other parts of the country had reopened.

Ms. Weingarten defended her members’ right to work safely and emphasized the importance of ventilation, but said she would strive to be clearer in the future that “kids have to be the priority.” That includes in-person instruction, she said.

“I thought I was pretty loud,” she added. “I would be even louder.”

Conflicting advice in 2020

Few education or health leaders doubt that it was right for schools to close in March 2020, when much about Covid-19 was unknown.

But by early that summer, there was a spate of evidence that pointed toward a careful reopening. Classrooms had reopened abroad, with research showing that there was limited spread of the virus inside schools. It was becoming clear that children tended to be less severely affected by the virus than many adults were, and that young children were less likely to spread the disease.

The American Academy of Pediatrics issued a report in June 2020 recommending that schools reopen. Republican-run states like Texas and Florida forged ahead with plans to offer in-person instruction to families who wanted it.

Yet thousands of schools in Democratic-majority states like California, Oregon, Washington and Maryland stayed closed or partially closed for another full year.

Policymakers who had a role in those decisions argue that applying evidence from abroad was difficult because of several factors, including higher U.S. infection rates, less consensus around masking and limited availability of virus tests.

The politicization of the pandemic also played a role. President Trump repeatedly called on schools to reopen, while many Democratic officials and advocacy groups fought for stricter safety measures and more federal aid to schools.

In addition, conflicting advice from health experts caused confusion.

The Centers for Disease Control had, at times, recommended greater precautions than the pediatrics academy did, including maintaining six feet of distance between desks. In the summer of 2020, health agencies in states like California advised schools to remain closed in areas where case levels were high — which was almost everywhere.

The California Department of Public Health declined to respond to questions about their approach to school closures for this article.

Becky Pringle, president of the National Education Association, the country’s largest teachers’ union, said that following cautious public health guidance was the right approach, and is the one she would follow again.

“What we needed to do was to listen to infectious disease experts,” Ms. Pringle said.

She pointed out that rates of infection and death were higher in low-income communities of color, and that many parents preferred to keep their children at home.

“You try to make the best decisions with the information you have,” she added.

Sean O’Leary, a pediatric infectious disease specialist at the University of Colorado and the lead author of the academy’s report, recalled that some teachers pushed back against the report’s recommendations by pointing to crowded classrooms, dated H.V.A.C. systems and sealed-shut windows in their schools, many of them in low-income urban neighborhoods.

The teachers argued that reopening schools would be dangerous, and they organized marches — outdoors and masked — to demand that classrooms remain empty until virus transmission rates fell essentially to zero.

Dr. O’Leary said it was clear even at the time that those demands failed to consider what he called “the bigger picture.”

“What are the downstream consequences of closing schools?” he asked. “Is this the right decision as a society?”

Local officials who wanted to reopen schools sometimes found that their plans were superseded by governors and state health officials.

Heidi Sipe, the superintendent in Umatilla, Ore., a rural district that serves mostly Hispanic and low-income students, remembered releasing a video detailing a complex reopening plan for her district in the fall of 2020, only for the governor to announce shortly afterward that all Oregon schools would be remote that fall based on infection rates.

“It was devastating for us,” she said. “The challenge of that was the organizational trust that was lost — because so many of our families lost faith.”

Oregon’s school strategy mirrored a cautious approach to the virus more broadly in many Democratic states. “I’m proud overall of our response,” said Dr. Dean Sidelinger, Oregon’s state health officer, who noted that Oregon had one of the lower Covid mortality rates in the country.

But research now suggests that keeping schools closed was not a significant factor in slowing the virus, particularly after other parts of society were up and running. More people died in some Republican regions, Dr. O’Leary said, “not because the schools were open, but because they didn’t wear masks and didn’t get vaccinated.”

Would leaders make different decisions today?

Almost everyone in education acknowledges that extended school closures were damaging. Academic achievement plummeted and has not recovered. Student absence rates are double their prepandemic levels. And remote learning pushed children further into screens and away from learning and play in the physical world.

But even today there is not broad consensus about whether the lengthy closures were necessary.

Brent Jones, superintendent of Seattle Public Schools, said he was “not apologetic” about his system’s 18-month period of virtual and hybrid learning, one of the longest in the country.

“I saw it as a forced opportunity to step back,” he said. “We were called upon, frankly, to expand our mission to include many other things: nutritional, social, emotional, mental health. There was a cry for support. Schools stepped into that gap.”

Seattle also made investments in ventilation that he said could help keep classrooms open during another pandemic.

In some other cities, ventilation remains a sticking point, particularly in old school buildings.

“We would insist that the buildings be safe before they are occupied,” said Arthur G. Steinberg, president of the teachers’ union in Philadelphia, where dozens of school buildings do not have updated H.V.A.C. systems.

Still, he and others said that they would be more apt to consider school closures on a building-by-building basis, rather than pushing for systemwide shutdowns.

Stacy Davis Gates, president of the Chicago Teachers’ Union, acknowledged that some city schools “could have probably been fine” reopening sooner, but noted that they tended to be the ones in more affluent neighborhoods.

“How do you continue to create a policy that marginalizes people who have been marginalized for years?” she asked in an interview late last year.

Ms. Weingarten, the national union leader, said that in a future crisis, she would urge local unions to come up with their own safety plans, and to be creative in order to educate children in person — an approach many parents were desperate for during the Covid shutdowns.

If school buildings do not have proper ventilation, she said, “then you find other buildings within the city.”

Still, politics, not logistics, may be the biggest obstacle in a future health emergency.

Public trust in science and schools fractured during the pandemic and remains low, especially among Republicans. Governors and state leaders could once again split along partisan lines. If anything, over the last five years, Americans’ views about vaccines, public health and education have only become more divided and politicized.

Some of the mistrust seeded by the pandemic has spilled over into other arenas of education.

Debates about schools now often focus on how race, gender and American history are taught. Republicans are pushing new state laws to provide public money for families to send their children to private schools. The number of children nationwide who are using some form of private-school voucher has doubled since 2019, to more than 1 million.

Partisans on both the right and left say those trends might not have taken off without the widespread anger and frustration arising from how the education establishment handled Covid-19.

Public health experts caution that their guidance in a future health crisis would depend on the particular disease. A future pathogen could be far more dangerous for children or teachers than Covid-19 was.

“We don’t know what could be coming,” said Sean Bulson, the superintendent of schools in Harford County, Md., outside Baltimore. But based on what was learned over the past five years, he said, “our threshold for closing probably got higher.”

Helyeh Doutaghi, a scholar in international law, began a new job in 2023 as the deputy director of a project at Yale Law School.

As an activist who had championed pro-Palestinian causes in both published papers and public appearances, Dr. Doutaghi seemed to fit into the left-leaning mission of the Law and Political Economy Project, which promoted itself as working for “economic, racial and gender equality.”

Last week, though, she was abruptly barred from Yale’s campus in New Haven, Conn., and placed on administrative leave. She was told not to advertise her affiliation with the university, where she had also served as an associate research scholar.

Yale officials cited the reason as allegations that she was tied to entities subject to U.S. sanctions. It was an apparent reference to Samidoun, a pro-Palestinian group placed on the U.S. sanctions list last year, after the Treasury Department designated it a “sham charity” raising money for a terrorist organization, the Popular Front for the Liberation of Palestine.

The decision came three days after a news site, powered at least in part by artificial intelligence, published a story about Dr. Doutaghi’s connections to the group.

The news site called her a member of a terrorist group, citing postings referring to appearances she made on panels at Samidoun-sponsored events, but a lawyer for Dr. Doutaghi said she is not a member of Samidoun, a global organization that sponsors meetings and protests supporting Palestinian causes.

In an interview, Dr. Doutaghi, 30, called herself a “loud and proud” supporter of Palestinian rights. “I am a scholar,” she said, adding, “I am not a member of any organization that would constitute a violation of U.S. law.”

The swift action against Dr. Doutaghi illustrates the tightrope American universities are walking as the Trump administration takes aim at higher education. Yale’s peer institution, Columbia, lost $400 million in federal funding last week after being named on a list of schools accused of tolerating antisemitism. On Monday, the Trump administration announced that Yale was among 60 schools that could face funding cuts if federal investigations show evidence that they have permitted antisemitic behavior.

In a statement Tuesday, Yale Law School described the allegations against Dr. Doutaghi as reflecting “potential unlawful conduct.”

“We take these allegations extremely seriously and immediately opened an investigation into the matter to ascertain the facts,” said the statement, issued by Alden Ferro, a spokesman for Yale Law. “Such an action is never initiated based on a person’s protected speech.”

Dr. Doutaghi said the actions against her are part of an attempt to silence scholars. “This is the type of thing that happens under fascist dictatorships, which Donald Trump is trying to establish,” she said in the interview.

The article about Dr. Doutaghi was published on March 2 on Jewish Onliner. On its website and on Substack, Jewish Onliner says it is “empowered by A.I. capabilities.” It does not identify any reporters on its site.

An effort to reach Jewish Onliner for comment elicited a response from “JO,” which identified itself as an A.I. assistant developed by Jewish Onliner. Later, emails from the site said that, while it uses A.I. to enhance research, fact-checking and rapid content creation, the final edits are done by humans.

The identities of the news site’s staff were kept private out of concern for “professional repercussions, doxxing, etc.,” the site said.

In January, the Israeli publication Haaretz questioned the reliability of such A.I.-powered platforms that it said worked to promote Israel’s cause online.

Eric Lee, the lawyer representing Dr. Doutaghi, also questioned the reliability of Jewish Onliner’s reporting in correspondence with Yale.

In his letter last week letter placing Dr. Doutaghi on administrative leave, Joseph M. Crosby, Yale’s senior associate dean, raised concerns about her activities. “As you are aware, the university is reviewing serious allegations regarding your activities with various entities that are subject to U.S. sanctions,” said the letter, dated March 5, which was reviewed by The New York Times.

Samidoun, based in Vancouver and London, says that its primary mission is to support Palestinian prisoners and to amplify the voices of Palestinian advocates of justice and human rights.

The impact of U.S. and European Union sanctions on Iran was the topic of Dr. Doutaghi’s dissertation for the Ph.D. she obtained from Carleton University in Ottawa, which was officially awarded after she joined the Yale project.

Amy Kapczynski, a Yale Law professor who co-founded the project, which is funded by outside grants, envisioned the project as an effort to understand the structures that led to the election of Mr. Trump and a counter to neoliberal thought in America, according to posts on its website. Ms. Kapczynski did not respond to a message seeking comment.

Dr. Doutaghi joined in October 2023, about a week before the Hamas attack on Israel. An Iranian and a Muslim, she said Yale knew about her views when they hired her.

“In fact, at the time I believed that this quality would be an asset for the project I was hired to help lead,” she said.

The Law and Political Economy Project appeared to embrace Dr. Doutaghi’s views, featuring her last year in a virtual event titled, “A Political Economy of Genocide and Imperialism.” The page describing the discussion has been scrubbed from the project website, but it referred to the “genocide in Palestine,” a characterization that some pro-Israel groups have called antisemitic.

Within 24 hours of the Jewish Onliner article’s publication, Dr. Doutaghi said, she began to receive harassing and threatening messages online. She was also asked to meet with Yale officials to explain her position. She decided to retain a lawyer, Mr. Lee, who is based in Southfield, Mich., and asked for additional time to prepare for the meeting with Yale because she was fasting for Ramadan and dealing with harassment.

But three days after the Jewish Onliner published its article, Dr. Doutaghi was barred from campus and placed on administrative leave by Mr. Crosby, who told her the move was necessary because “we have not received any responses or factual explanations from you.”

Mr. Lee said he hoped Dr. Doutaghi’s job and access to emails and campus would be restored, and he is asking the school to take “public action to restore her reputation.”

Just a few years ago, university statements on the day’s social and political issues abounded.

When Russia attacked Ukraine in 2022, Harvard’s president at the time called it “senseless” and “deplorable,” and flew the invaded country’s flag in Harvard Yard. After George Floyd died under the knee of a white police officer, Cornell’s president said she was “sickened.” The University of Michigan’s president described the Oct. 7, 2023, violence against Israel as a “horrific attack by Hamas terrorists.”

But over the last year, each of those universities has adopted policies that limit official statements on current issues.

According to a new report released on Tuesday from the Heterodox Academy, a group that has been critical of progressive orthodoxy on college campuses, 148 colleges had adopted “institutional neutrality” policies by the end of 2024, a trend that underscores the scorching political scrutiny they are under. All but eight of those policies were adopted after the Hamas attack.

“We must open the way for our individual faculty’s expertise, intelligence, scholarship and wisdom to inform our state and society in their own voice, free from institutional interference,” said Mark Bernstein, a regent at Michigan, after adopting the policy in October.

He said the university had historically refrained from issuing statements on momentous events, like the assassinations of Abraham Lincoln and John F. Kennedy or during the two world wars.

“So institutional statements are a modern phenomenon and a misguided venture that betrays our public mission,” he said.

The universities are adopting such policies at a time when the Trump administration has moved aggressively to punish them for not doing enough to crack down on antisemitism and for embracing diversity, equity and inclusion policies.

On Friday, the administration announced that it was pulling $400 million from Columbia, a move that sent shock waves across higher education. The administration has already said it is looking to target other universities.

Universities ramped up issuing statements on hot-button issues about a decade ago, after the rise of the Black Lives Matter movement and the police shootings of Black people in places like Ferguson, Mo., said Alex Arnold, director of research at the Heterodox Academy.

Some conservatives had long lamented such statements and believed they veered too leftward. Speech groups like the Foundation for Individual Rights and Expression worried that they discouraged dissent. For a while, the statements were hardly the subject of widespread controversy.

The Hamas attack and the war that followed changed the equation.

The Israeli-Palestinian conflict has always split the left, but the attack on Oct. 7 and the war that followed sharpened those divisions. The statements that universities issued on the attack and Israel’s bombing of Gaza came under scrutiny, and were often criticized for being too late, too weak, too biased — or all three.

University leaders, under pressure from donors, lawmakers and the public, began to ask: Why put out statements at all?

About four out of five colleges that adopted neutrality policies are public and face scrutiny from state lawmakers. Several states, including Texas and Utah and North Carolina, forced their public universities to adopt such policies. Others, like Tennessee, are considering it.

Most of the new policies apply to senior administrators, like college presidents and provosts. Others also encompass units like academic departments. And many apply to faculty members when they are speaking in an official capacity, but often make clear that faculty are free to express personal views, according to the Heterodox Academy.

“The whole experience of coping with the campus controversy triggered by the Hamas attack has really gotten institutional leaders to think carefully and to reflect on what the function of our institutions of higher education is,” Mr. Arnold said. “I do think this is probably going to be a pretty durable change.”

Critics of the neutrality trend have argued that administrators are merely sidestepping difficult debates on the Middle East conflict, and scared of angering donors and lawmakers.

After Clark University, in Massachusetts, said it would shy away from taking positions, the school newspaper’s opinion editor called the move a “fake policy” designed to curb discussion of the conflict.

But even universities that adopted such a policy have not gone totally silent on contested political issues.

At an Anti-Defamation League event in New York City last week, Michigan’s president, Santa Ono, called the effort to boycott, divest and sanction Israel antisemitic, and said his response had been to invest even more in those partnerships.

In an email, the university said the new neutrality policy adopted a “heavy presumption” against issuing statements “not directly connected to internal university functions.”

“Combating antisemitism and making sure we have an environment where all students can thrive and succeed is part of our moral and legal obligation, and absolutely connected to our internal functions as an institution of higher education,” said Colleen Mastony, a Michigan spokeswoman.

Presidents are often stumbling over their new policies. During an October interview with the school newspaper, Harvard’s president, Alan Garber, called a statement by pro-Palestinian students “offensive,” prompting the editorial board to tell him to “follow your own policy.”

Last month, the American Association of University Professors, a faculty rights group, issued a statement on neutrality that was, more or less, neutral. It stated that the idea “is neither a necessary condition for academic freedom nor categorically incompatible with it.”

The re-election of Donald Trump is now testing those policies.

As the new administration, which has described universities as “the enemy,” ratchets up its attack on higher education, colleges are under greater pressure to be voices of resistance.

But many college presidents have been spooked into silence, said Patricia McGuire, president of Trinity Washington University, a small Catholic institution three miles from the White House.

“They look at what happened to Claudine Gay, and some of the other presidents,” she said, referring to the former Harvard president who resigned last year after a congressional hearing on antisemitism. “And they’re like: ‘I don’t want that to happen to me. So I’ll just shut up and hunker down, and hope this cloud passes.’”

No university is more associated with neutrality than the University of Chicago, where incoming students are furnished with the Kalven Report, the 1967 document that made the case for neutrality. The report, penned as violence upended college campuses during the Vietnam War, said the university “is the home and sponsor of critics; it is not itself the critic.”

Tom Ginsburg, director of the Forum for Free Inquiry and Expression at Chicago, says adopting neutrality signals to lawmakers that colleges are committed to welcoming diverse viewpoints.

“Because the statements tended to reflect the majority views on campuses, which are overwhelmingly left-leaning,” he said, “you can see how adopting it would be a way of saying to lawmakers: ‘This isn’t who we really are. We’re not indoctrinating people with contested positions.’”

But even the Kalven Report included a caveat that doesn’t settle precisely when universities should issue statements. Neutrality, the report says, still allows colleges to speak out when “the very mission of the university and its values of free inquiry” are threatened.

That moment is now, said Ms. McGuire of Trinity Washington University. “The erosion of knowledge and expertise that this administration has embraced is very, very scary,” she said, “and higher ed should be calling it out at every turn.”