“The challenge facing our schools is unprecedented,” said candidate Joe Biden last July. “President Trump has made it much worse. We had a window to get this right. And Trump blew it.”

Now, President Biden has his own window to get it right when it comes to safely reopening schools. And he’s stumbling a bit, caught in a crossfire between parents and teachers about when and how to proceed.

As The Washington Post reported: “Many parents, including those in politically crucial suburbs, crave the normalcy that will come with the reopening of classrooms, which have been closed for nearly a year in much of the country. But few groups did more to push Biden’s candidacy than teachers’ unions, which have resisted returning to school buildings in communities across the country.”

Republicans have reacted gleefully, sensing an issue that can damage Democrats in next year’s elections while concealing the splits in their own ranks over Trump’s future. A recent Quinnipiac poll shows they might be on to something. While 58% backed Biden’s general approach to the pandemic, only 42% expressed approval for how he’s “handling the reopening of schools.”

“This is going to be a huge issue, one of the defining issues, when we get to November 2022,” Minnesota Rep. Tom Emmer, who chairs the National Republican Congressional Committee, told CQ Roll Call. “It’s going to be very easy for us to point out that Democrats ignored the science and stood with their special-interest donors instead of with students.”

An early test could come this year in Virginia, where Republican Pete Snyder is running for his party’s gubernatorial nomination by stressing the school issue in his early TV ads. “I think Virginia is the beginning of the nationwide earthquake on this issue,” he told NBC.

Democrats worry he could be right. Ed Rendell, a Biden ally who served as both mayor of Philadelphia and governor of Pennsylvania, warned the president to show toughness. “Tell your friends: ‘Look, I’ll listen to you. I’ll try to abate your concerns. But once I’ve done all that, I’m going to go forward,’ ” Rendell said in the Post.

Education is more a local than a federal issue. Washington’s main role is funding, and Biden is doing what he can on that front, pushing a relief bill through Congress that contains $130 billion for struggling school systems.

But a president’s tone and priorities also matter, and Biden’s clearly vulnerable to the GOP attacks. After all, his wife once belonged to a teachers’ union and he’s a totally unabashed supporter of organized labor. As he likes to put it, “I am a union guy — beginning, middle and end.”

It’s not just Republicans who are faulting the teachers’ unions for keeping classrooms closed. In Chicago, to take one example, liberal Democratic Mayor Lori Lightfoot has been fighting a guerilla war with the city’s educators. In a recent interview with The New York Times, she bitterly assailed the union, saying, “I think, ultimately, they’d like to take over not only Chicago Public Schools, but take over running the city government.”

This battle is not just about the raw exercise of power, however. Biden said often during the campaign that he would let science, not politics, dictate his policies, and scientific evidence is starting to conflict with his loyalty to the unions. His own director of the Centers for Disease Control and Prevention, Rochelle Walensky, concluded recently that there was “increasing data to suggest that schools can safely reopen.”

That view was strongly reinforced by a New York Times survey of 175 pediatric infectious disease experts, who contradicted union orthodoxy by largely agreeing that “it was safe enough for schools to be open to elementary students for full-time and in-person instruction now.”

One of those experts, Dr. David Rosen of Washington University in St. Louis, said, “There is no situation in which schools can’t be open unless they have evidence of in-school transmission.”

Moreover, the experts stressed, the health damage the virus might cause has to be balanced against the enormous emotional and psychological damage done to students who are kept out of school.

“The mental health crisis caused by school closing will be a worse pandemic than COVID,” said Dr. Uzma Hasan of RWJBarnabas Health in New Jersey.

“This is devastating a generation,” added Dr. Susan Lipton of Sinai Hospital in Baltimore.

Biden was right to criticize Trump for not relying on science. Now he has to listen to the experts and defy the teachers’ unions — or pay the political price.

Steven Roberts teaches politics and journalism at George Washington University. He can be contacted by email at stevecokie@gmail.com.