President Donald Trump on Wednesday threatened to withhold federal funding if schools don’t reopen in the fall, and he lashed out at federal health officials over school reopening guidelines that he says are impractical and expensive.

Taking to Twitter to voice his frustration, Trump argued that countries including Germany, Denmark and Norway have reopened schools “with no problems.” He also repeated his claim that Democrats want to keep schools closed for political reasons and not because of any risks associated with the coronavirus.

“The Dems think it would be bad for them politically if U.S. schools open before the November Election,” Trump said, “but is important for the children & families. May cut off funding if not open!”

He did not immediately say what funding he would cut off or under what authority.

Trump made the comments a day after launching an all-out effort pressing state and local officials to reopen the nation’s schools and colleges this fall. At a White House event Tuesday, health and education officials argued that keeping students out of school for the fall semester would pose greater health risks than any tied to the coronavirus.

Among those pushing for a fall reopening was the chief of the Centers for Disease Control and Prevention. But Trump on Wednesday said the agency’s school guidelines are “very tough & expensive.”

“While they want them open, they are asking schools to do very impractical things. I will be meeting with them!!!” Trump wrote.

The CDC’s director, Dr. Robert Redfield, had emphasized that his agency’s guidelines were only recommendations, and he urged schools to find ways to reopen while minimizing the spread of COVID-19.

“Nothing would cause me greater sadness than to see any school district or school use our guidance as a reason not to reopen,” Redfield said.

The CDC’s guidance recommends that students and teachers wear masks whenever feasible, spread out desks, stagger schedules, eat meals in classrooms instead of the cafeteria, and add physical barriers between bathroom sinks.

Trump did not clarify which of the guidelines he opposed.

The White House’s task force on the coronavirus was meeting at the Education Department on Wednesday, emphasizing the administration’s push to reopen schools.

At the White House event, Trump took aim at Democrats who he says are standing in the way of a fall reopening. “They think it’s going to be good for them politically, so they keep the schools closed,” Trump said. “No way. We’re very much going to put pressure on governors and everybody else to open the schools.”

He added that parents and children want schools to reopen, declaring that “it’s time to do it.”

But that bright outlook was met with skepticism by some beyond the White House. The president of the nation’s largest education union said Trump is more interested in scoring points for the November election than in keeping students safe.

“Trump has proven to be incapable of grasping that people are dying — that more than 130,000 Americans have already died,” said Lily Eskelsen García, president of the National Education Association. “Educators want nothing more than to be back in classrooms and on college campuses with our students, but we must do it in a way that keeps students, educators and communities safe.”

Trump’s claim that Democrats are pressing to keep schools closed for political reasons has been criticized by health experts who say politicizing the issue makes it more difficult to work toward reopening schools.

“When you make it about politics and just people trying to score points and get elected, I mean, I really think it’s a disservice to how incredibly important this issue is,” Jennifer Nuzzo of Johns Hopkins University’s COVID-19 Testing Insights Initiative said in an interview. “And it really distracts from what I think we need, which is real solutions and a plan in order to make this happen.”

Whether schools and colleges should open this fall and how has been a topic of growing tension as the coronavirus continues to surge in parts of the United States. Trump applauded Florida Gov. Ron DeSantis for his state’s recent order to open public schools this fall. The president attacked Harvard University for its decision to hold instruction online for the fall term.

Some public schools have announced plans to bring students back for only a few days a week, an option that Education Secretary Betsy DeVos on Tuesday said was unacceptable.

“It’s clear that our nations schools must fully reopen and fully operate this school year. Anything short of that robs students, not to mention taxpayers, of their future,” DeVos said.

During a call with governors Tuesday, DeVos slammed plans by Virginia’s Fairfax County Public Schools to have families decide between fully remote instruction or two days a week at school. “A choice of two days per week in the classroom is not a choice at all,” DeVos said, according to audio of the call obtained by The Associated Press.

The American Academy of Pediatrics recently issued guidelines suggesting that schools aim to start the academic year “physically present in school.” Keeping students at home can lead to social isolation, the organization said, and prevent schools from identifying learning deficits, abuse, depression and other issues.