Marshall Tuck is the last person you would expect to say it’s time to limit charter schools.

Tuck, a Democratic candidate for California schools superintendent, once oversaw a network of charter schools in Los Angeles and was heavily backed by the state’s charter lobby when he ran for (and narrowly lost) the post in 2014.

That’s why it’s surprising that one of Tuck’s first major policy announcements in his latest bid was a push to ban for-profit charter schools in California, a top priority of teachers unions.

“Educators — whether at district or charter public schools — can agree: public schools must serve students, not shareholders,” Tuck wrote. “Profit has no place in our public schools, and I urge politicians in Sacramento to make that the law.”

This fresh hostility toward for-profit charter schools extends beyond California. Across the country, more left-of-center charter school advocates are distancing themselves from for-profit charter schools. Some want to prohibit them outright.

Jeff Henig, a Columbia professor, sees this as a symptom of a broader rift, driven in part by the election of Donald Trump and appointment of Secretary of Education Betsy DeVos, who has backed private school vouchers and for-profit charter schools.

“What may account for why this is becoming more publicly talked about is this re-opening what was always a strange-bedfellow coalition,” he said. “That cleavage is widening now, with the for-profits seeing a chance under Trump and DeVos to jump back ahead in the game and the nonprofit, progressive group worrying that they’ll be tarred by the bad-apple stories.”

In most places, charter schools are required to be run by nonprofit boards, but operations and management can be turned over to for-profit companies, often known as education-management organizations or EMOs, though some states bar this practice. As of 2014, about one in five charter students attended a school run for profit.

For years, the charter school movement was characterized by a relatively amicable alliance between progressive and conservative education reformers, with disagreements about vouchers and for-profit charters largely playing out behind the scenes.

“Those folks for many years traveled together because their main battle was against the unions and traditional public schools, and the stickiness of the status quo,” Henig said. “But there never was a meeting of the minds really among all of the charter proponents.”

For progressive charter advocates, keeping an arm’s length from for-profit charter schools may be smart politics.

“[California] is a very blue state, and an anti-for-profit position is almost certainly a majority or strong plurality opinion,” said Morgan Polikoff, an associate professor at the University of Southern California, about Tuck specifically. “Especially given current national politics and the views of Betsy DeVos, this position allows him to separate himself from unpopular folks in Washington.”

Nick Melvoin, a successful candidate for L.A. school board who was endorsed by pro-charter groups, joined Tuck’s push. “We need to pass this legislation banning for-profit schools to combat the radical anti-public education agenda of Betsy DeVos and Donald Trump,” he wrote.

Shavar Jeffries of Democrats for Education Reform told Chalkbeat in a recent interview, “We’re categorically opposed to for-profit providers running schools.”

John King, the former secretary of education and founder of a charter school in Boston, expressed a similar view.

“I would distinguish between the role that high-performing public charters can play in a strong public education system as opposed to vouchers and for-profit charters. I believe public dollars should go to public schools with public accountability,” King, who is currently president and CEO of EdTrust, told Chalkbeat.

“In New York, when we raised the charter cap in 2010 we banned new for-profit charters,” he added. “That seemed right to me. I would be fine with other states taking a similar approach.”

To those who favor a free-market approach, including many advocates of school vouchers, the criticism of for-profit schools is a mistake that could limit options for students who need them.

“I’m from the Malcolm X school — by any means necessary,” said Kevin Chavous of the American Federation for Children, the school choice group that Betsy DeVos used to lead. “I don’t rule out any learning modality that can help a kid.” (Chavous is on the board of K12, a for-profit virtual school operator.)

DeVos echoed that view last week in testimony before the U.S. Senate.

“Whether it’s a for-profit managed institution or a not-for-profit, if students are achieving and parents are making those choices on behalf of their children, I think those are the better measures to be oriented around,” DeVos said.

So how strong is the case against for-profit charters?

On one hand, studies comparing for-profit schools to nonprofits and traditional public schools in the same area don’t find consistent differences in performance, as measured by test scores. Nationally, as well as in Florida and Michigan, for-profit charter schools perform comparably or even a bit better.

For-profit charters do spend significantly more on administrative costs — and less on classroom instruction — than nonprofits according to one recent study, consistent with concerns about profiteering. But the authors said there is little evidence that those schools were less effective or efficient as a result.

On the other hand, the largely for-profit sector of virtual charter operators have harmed student achievement — often dramatically, according to multiple studies. They have also proven politically influential, in a way that critics say helps keep struggling schools open.

An extensive analysis of charter schools in North Carolina found that the practice of contracting management out to for-profit companies likely violates the law. The nonprofit KIPP charter schools in the state, by contrast, had governance practices that were “thorough, correct, and in compliance.”

Bruce Baker, a Rutgers professor and frequent charter school critic who has examined financial malfeasance in the sector, said the distinctions between the sectors weren’t always clear.

There are “bad actors on both sides,” he said, “but most good actors [are] on [the] nonprofit side.”