WASHINGTON (NYTIMES) - US President Donald Trump pressured the government's top public health experts on Wednesday (July 8) to water down recommendations for how the nation's schools can reopen safely this fall and threatened to cut federal funding for districts that defied his demand to resume classes in person.

Once again rejecting the advice of the specialists who work for him, Mr Trump dismissed the Centres for Disease Control and Prevention's "very tough & expensive guidelines", which he said asked schools "to do very impractical things".

Within hours, the White House announced that the agency would issue new recommendations in the days to come.

The president's criticisms, in a barrage of Twitter threats, inflamed a difficult debate that has challenged educators and parents across the country as they seek ways to safely resume teaching American children by September.

Even as the coronavirus is spreading faster than ever in the United States, Mr Trump expressed no concern about the health implications of reopening in person and no support for compromise plans that many districts are considering.

His all-or-nothing stance left him at odds with the nation's two largest school districts.

Mayor Bill de Blasio of New York City announced shortly after Mr Trump's tweets that schools would not fully reopen in September, with students attending classes in person only one to three days a week to accommodate social distancing. The chief public health officer in Los Angeles County told school officials on Tuesday to be prepared to continue learning entirely from home given the surge of infections in California.

But Mr Trump's attack on the CDC underscored his growing impatience with public health experts he considers obstacles to his ambitions of reopening the country after months of lockdown.

As he significantly trails Joe Biden, his presumptive Democratic challenger, in most polls, the president has brushed off warnings and pushed states to reopen businesses in hopes of reviving the crippled economy before the election on Nov 3, a goal that would be hamstrung if parents had to remain at home with their children this fall.

"I disagree with @CDCgov," Mr Trump wrote on Twitter on Wednesday, a day after hosting a series of calls and events to pressure schools to reopen fully. "While they want them open, they are asking schools to do very impractical things. I will be meeting with them!!!"

During a coronavirus task force briefing later on Wednesday afternoon, Vice-President Mike Pence announced that the CDC would issue new recommendations next week, saying the guidelines should not be a reason for schools to stay closed.

"We just don't want the guidance to be too tough," he said, promising "five different documents that will be giving even more clarity on the guidance going forward".

The agency has recommended for weeks that schools that remain open modify layouts to maintain social distancing, install physical barriers where that is not possible, increase disinfection and cleaning of facilities, avoid serving communal meals in cafeterias, discourage sharing objects and ensure ventilation systems are up-to-date. If a school has a confirmed case, the guidance says, students and "most staff" should be dismissed for two to five days while local health officials consider what to do next.

An administration official, who discussed internal deliberations on condition of anonymity, said the new guidance had been in development for weeks but had yet to be cleared by top CDC or task force officials. The guidelines would address how schools can reopen and whether parents should send children, most likely including a checklist for making that decision. The official denied that Mr Trump or other White House officials had pressured the agency to ease the existing guidelines for schools, which were updated in April.

Another official said that some in the White House had learnt of the CDC's plans to distribute new guidance only on Tuesday, when Dr Robert Redfield, the agency's director, told governors about it in a call led by Mr Pence. Dr Redfield said on Wednesday that Americans should not interpret CDC guidelines as requirements.

Dr Anthony Fauci, the nation's top infectious disease expert and one of the coronavirus task force's most prominent members, did not attend the briefing on Wednesday, an absence that drew attention.

Dr Fauci later said in a brief telephone conversation that he was part of a small group of officials asked to call in from the White House Situation Room to a meeting the task force held before the briefing. Dr Fauci said the officials who called in were less relevant to the topics discussed in the briefing.

In taking on defiant educators, Mr Trump invoked the one lever he had - federal funding - to impose his will on schools, which are traditionally run by localities and states.

"In Germany, Denmark, Norway, Sweden and many other countries, SCHOOLS ARE OPEN WITH NO PROBLEMS," Mr Trump wrote on Twitter. "The Dems think it would be bad for them politically if US schools open before the November Election, but is important for the children & families. May cut off funding if not open!"

In reality, it may be a hollow threat. The president has no control over about 90 per cent of school district budgets, which are generally financed by local property and sales taxes. And he has little control over federal funding already appropriated by Congress.

"Trump has no legal authority to withhold funds," Mr Arne Duncan, the secretary of education under President Barack Obama, said during a briefing with reporters on Wednesday. "Threatening people, bullying them, lying doesn't stop the virus from spreading."

He added: "It's ludicrous. It'd be funny if it wasn't so sad."

The Education Department may be able to reroute or withhold some emergency coronavirus relief funding that school districts say they desperately need to fund staff, programming and the public health measures recommended by the CDC. And the president could veto additional funds that schools want from Congress this summer.

On Wednesday, Ms Kayleigh McEnany, the White House press secretary, said Mr Trump would seek to "substantially bump up money for education" in the next coronavirus relief package, but "this money should go to students".

A senior House Democratic aide said lawmakers would most likely push to limit the president's authority to withhold school funds in a next round of relief.

Many parents, educators and doctors believe that the social, educational and psychological costs of a prolonged shutdown or online learning now outweigh the risk of the virus itself, a position expressed by the American Academy of Pediatrics. But how schools reopen safely is a matter of serious discussion.

While children have proved less susceptible to the virus, teachers are more vulnerable because of their age. Many have expressed concern about returning to work in buildings that were never intended to keep children 6 feet apart or otherwise prevent the spread of a deadly virus.

Dr Deborah Birx, the White House coronavirus response coordinator, said the mortality rate for those 25 and younger was less than a tenth of a per cent, though she cautioned there was much to learn.

"Until we know how many have been infected, we have no evidence that there is significant mortality in children without coexisting diseases," she said.

But she added that children might be a threat to relatives in multigenerational homes.

"Americans have done a great job in keeping infection rates low in children in the sheltering time," she said. "We are worried now that as cases spread that it is getting to the older parents and the grandparents."