In November, Sen. Elizabeth Warren traveled to Clark Atlanta University to give a speech about the history of discrimination against working black women. Instead of receiving a unanimous welcome, Warren was repeatedly interrupted by a group of pro-charter-school demonstrators — mostly black women — chanting, “Our children, our choice!” A few hours later, having agreed to meet with the protesters if they let her finish her speech, the then-presidential candidate found herself listening to a Memphis activist named Sarah Carpenter explain her deep unhappiness with Warren’s education platform.

Warren’s plan called for quadrupling funding for the federal Title I program, which supports high-poverty schools, and spending billions to help students with disabilities. But it was the charter-school section that had driven Carpenter and dozens of fellow parents to raise money on GoFundMe for a bus to Atlanta.

The experience of watching her children and grandchildren fail in the Memphis public school system — and then succeed at KIPP, a national chain of nonprofit charter schools — had turned Carpenter into a charter-school champion. And for most of her 20 years as an education advocate, charter schools had enjoyed steady, bipartisan political support. The conservative Walton Family Foundation, which has spent hundreds of millions of dollars promoting market-oriented education policies, financially supported Carpenter’s nonprofit organization, which counsels parents on selecting schools for their children. But the previous months had been increasingly difficult for supporters of “school reform,” a set of policies that broadly includes holding schools accountable for student scores on standardized tests, tying teacher hiring and pay to their performance in the classroom, government intervention in persistently low-performing schools, and giving parents more publicly financed options through such policies as vouchers and charter schools.

Warren, for one, had been increasingly opposed to charter schools. In 2016, she opposed a Massachusetts ballot measure that would have lifted a statutory cap on the number of charter schools in the state, despite evidence that those in the Boston area were, on average, far more effective at educating poor children and students of color than regular public schools. In her presidential platform, Warren described her opposition to charters as fighting back against “privatization, corporatization, and profiteering in our nation’s schools.” In substance, her plan left existing nonprofit charters mostly alone while eliminating a federal charter funding program and banning for-profit charters. In tone, it tarred charter schools with phrases like “corruption,” “dark money” and “self-dealing.”