When Democratic presidential candidate Elizabeth Warren rolled out her plan for K-12 education, the proposal to eliminate federal funding for charter schools drew gasps from school choice supporters, including Democrats who've backed the education reform movement of the last decade, and cheers from teachers unions.

The responses were predictable, even if the proposal itself was not.

On one side, charter school advocates lashed out at the Massachusetts senator, calling her $800 billion plan, which also included a proposal to walk back high-stakes testing, a desperate attempt to earn the endorsement of the two national teachers unions.

"The thing that's stunning about this is she is sort of portraying herself in so many of her other policies as taking on a David and Goliath fight, standing against all the big forces that control the little guys," Amy Wilkins, the senior vice president of advocacy at the National Alliance for Public Charter Schools, says. "And with this she did a total flip and is lining herself up with the biggest donor to the Democratic Party, teachers unions, and kicking poor kids to the curb."

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On the other side, the 3.2-million member National Education Association and the 1.7-million member American Federation of Teachers, fawned over the proposal, saying it shows politicians are paying attention to the educators who have rallied, protested and went on strike in more than a dozen places this year over issues of pay , class size, support staff and the creep of charter schools.

"She gets it," AFT president Randi Weingarten said of Warren, who stood beside the union president and addressed tens of thousands of teachers in Chicago on Day Four of a citywide strike. If she's elected president, Weingarten said, "We won't be in the streets, we will be in our schools making America what it ought to be."

With the plan, Warren becomes the Democratic primary candidate with the most aggressive proposal against charter schools, though she's far from the only one with an anti-charter stance. Vermont Sen. Bernie Sanders ' K-12 plan calls for no new federal funding for charter schools and a wholesale ban on for-profit colleges. Former vice president Joe Biden has also called for a ban on for-profit colleges, which account for just 15% of all charter schools.

The pushback on display by the three Democratic front-runners stands in stark contrast to the course the Obama administration took, which oversaw an enormous expansion of the sector, pressing states and school districts to lift their caps on charters and replicate successful ones as a way to turn around low-performing school districts.

When former President Barack Obama and Biden entered the White House in 2008, roughly 1.4 million students were enrolled in 4,600 charter schools, according to the National Alliance for Public Charter Schools . By the end of the administration, more than 3 million students were enrolled in 7,000 of them. The strategy was overseen by former education secretaries Arne Duncan, who followed a similar playbook while CEO of Chicago Public Schools, and John King, who himself founded a charter school in Boston.

But today, the pendulum is swinging hard in the opposite direction, driven in large part by the two national teachers unions and by the ongoing educator unrest.

If Warren is elected president, however, the teachers unions may come to find her understanding of the charter sector is more nuanced than the pitch itself.

Warren believes charter schools should be subject to the same accountability and transparency as their surrounding traditional public schools, an aide for the candidate clarified, adding that Massachusetts' successful charter schools are a result in no small part from the state's strict charter laws.

Indeed, Massachusetts has one of the highest-performing charter sectors in the entire country and its charter law sets one of the highest bars for accountability and transparency.

For all the attention her proposal drew, it is consistent with her views on charter schools, Warren's aid said. That includes her 2016 vote against a ballot measure that would have raised the cap on charter schools in Massachusetts. At the time, Warren expressed concern about the impact that unfettered growth of charter schools has on school districts and traditional public schools.

"Many charter schools in Massachusetts are producing extraordinary results for our students, and we should celebrate the hard work of those teachers and spread what's working to other schools," Warren said in 2016 as she voted to oppose the ballot measure. "But after hearing more from both sides, I am very concerned about what this specific proposal means for hundreds of thousands of children across our Commonwealth, especially those living in districts with tight budgets where every dime matters. Education is about creating opportunity for all our children, not about leaving many behind."

Going forward, Warren's aide said, she is supporting the NAACP's recommendations, which suggest that school districts – rather than states – serve as charter organizers and that they be allowed to reject charter applications that do not meet the transparency and accountability guidelines that traditional public schools do, consider the strain on district resources caused by charter schools and establish policies regarding the oversight of charter schools.

Those who have been studying the influence of money on education policy and politics and the changing attitudes on the most contentious education policies, like charter schools, weren't as surprised by Warren's proposal, chalking it up to the constant teetering of the public discourse over what has long been one of the most divisive issues in K-12 education.

"This was a program that I think arguably was important both symbolically and substantively when it was initiated back in the 1990s, because then no one really knew whether charters would be able to launch to the degree to which they have," Jeffrey Henig, political science and education professor at Columbia University's Teachers College, says.

"The scale of the charter movement and its momentum and its alternative ways to fund itself is so much more expansive today," he says. "I can understand how you'd look at that program, especially if you are trying to signal that your priority is traditional public schools and not calling for the elimination of charters, but calling for at the very least the slow down in the expansion of charters, that this makes a certain amount of sense."

He underscored that the $340 million federal Charter Schools Program is a drop in the bucket compared to the revenue streams available to charter schools and their operators today. Eliminating it, he says, wouldn't cripple the entire sector.