Sen. Elizabeth Warren promised Monday that she would choose a former public school teacher as secretary of education if she was elected president.

“Let’s get a person with real teaching experience,” she said in an email to supporters. “A person who understands how low pay, tattered textbooks, and crumbling classrooms hurt students and educators.”

Warren’s announcement was a sign of how Betsy DeVos, President Donald Trump’s education secretary, has become a rallying point for Democrats on the campaign trail — a figure who, more than any other Trump administration figure, draws boos and hisses at Democratic rallies across the country.

DeVos, who has been a lightning rod since the day of her confirmation hearing in January 2017, has been criticized by Democrats for a lack of experience in public education. A wealthy Trump donor, she spent a career as a philanthropist promoting the expansion of charter, private, and religious schools in Michigan.

“I’ll just be blunt: Betsy DeVos is the worst Secretary of Education we’ve seen,” Warren told supporters in the email. “She and her team are up to their eyeballs in conflicts of interest. Instead of championing our students, they protect for-profit colleges that break the law and cheat them.”

Warren made the promise ahead of a town hall in Philadelphia with members of the American Federation of Teachers, an influential teachers union that has played host to Democratic candidates like Sens. Bernie Sanders and Kamala Harris. Teachers unions are a key constituency for Democrats vying for the presidency; Harris has courted them with a pledge to spend billions of dollars to raise teacher salaries nationwide.

Warren, the 69-year-old Massachusetts senator, has made her presidential campaign a sweeping call for the “big, structural change” needed, she says, to root out corruption and rewire a government and political system that serves corporate interests. Her campaign operation — from the shape of her events, driven by questions from the audience, to her decision to reject high-dollar donations — is designed, her aides say, to “demonstrate substance” behind the candidate and the many policy proposals she’s released.

Her vow to select a public school teacher as her education secretary is a promise made in concert with other promises she has made on education, including a promise of free universal childcare and a $1.25 trillion billion higher education plan that would cancel large swaths of student debt and offer free public college.

“Let’s get a person with real teaching experience,” Warren said in her email. “A person who understands how low pay, tattered textbooks, and crumbling classrooms hurt students and educators. A person who understands the crushing burden of student debt on students and young professionals and who is committed to actually doing something about it.”