WASHINGTON – President Donald Trump on Wednesday pressured the government's top public health experts to water down recommendations for how the nation's schools could reopen safely this fall and threatened to cut federal funding for districts that defy his demand to resume classes in person.

Once again rejecting the advice of the specialists who work for him, Trump dismissed the CDC'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 by September. Even as the corona­virus is spreading faster than ever in the United States, 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 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 Tuesday to be prepared to continue learning entirely from home given the surge of infections in California.

But 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 his Democratic challenger in most polls, the president has brushed off warnings and pushed states to reopen businesses in hopes of reviving the 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," 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 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 of objects and ensure ventilation systems are up-to-date. If a school has a confirmed case, the guidance says, students and "most staff" members 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 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 learned 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 Pence. 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 Wednesday, an absence that drew attention. 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. Fauci said the officials who called in were less relevant to the topics discussed in the briefing.

In taking on defiant educators, 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," Trump wrote on Twitter. "The Dems think it would be bad for them politically if U.S. schools open before the November Election, but it 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% 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," Arne Duncan, the secretary of education under President Barack Obama, said during a briefing with reporters 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. And the president could veto additional funds that schools want from Congress this summer.

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.