By picking Betsy DeVos — a billionaire education philanthropist and activist — as his education secretary appointee, President-elect Donald Trump sent a strong message about what his education priority will be: school vouchers.

Unlike others Trump was reportedly considering for the post, including education reform advocate Michelle Rhee and former state superintendents from Indiana and Florida, DeVos has never been formally involved with public education. She hasn’t been a teacher or principal, or run a school district or state education agency. She’s never even taken a public position on Common Core, the education standards that Trump railed against on the campaign trail.

But DeVos has a long history of activism on one issue: school choice — a term that refers to both school vouchers, which allow parents to use taxpayer money to send their children to private school, and charter schools, which are publicly funded but privately run.

Choosing DeVos suggests that Trump is putting school choice, and particularly vouchers, at the heart of his education agenda, rather than anything to do with higher education. But DeVos will have less power than President Obama’s two education secretaries, John King and Arne Duncan, in trying to carry out Trump’s plans.

Betsy DeVos is a Republican Party leader turned education activist

DeVos, who lives in Michigan, was a Republican Party activist before she turned her attention. She chaired the state’s Republican Party from 1996 and 2000; she was also a prolific fundraiser for George W. Bush in 2004 and for Republican Senate campaigns during the Bush administration. (Incidentally, she is married to Dick DeVos, an heir to the Amway fortune, one of the multilevel marketing schemes that recently attracted attention from HBO’s John Oliver.)

But in recent years, much of her time, energy, and money have been devoted to school choice. DeVos supports both charter schools and school vouchers, but vouchers — which allow parents to opt out of public schools entirely by providing public assistance to parents to send their children to private and sometimes religious schools — are more politically polarized. While charter schools draw support from both Republicans and Democrats, vouchers are overwhelmingly a right-of-center priority.

And DeVos is a voucher advocate first and foremost, advocating both for vouchers for children and for tax credits to businesses that give money to private school scholarship funds. She and her husband founded All Children Matter, a political action committee that supports school vouchers and private school scholarships, and she chairs the American Federation for Children, which advocates for the same issues.

Voucher programs, though, have been established at the state level — most education funding in the US is state and local, and despite efforts from congressional Republicans, Congress has never instituted a national school voucher program. Trump has vowed to try, and his nomination of DeVos suggests that he’s serious.

Trump’s plan for his first 100 days includes the creation of a $20 billion school choice program. The money — which is more than the Education Department currently spends on supporting K-12 education for poor students, and which Trump says would be found by “reprioritizing existing federal dollars,” meaning budget cuts elsewhere — would go to states with laws that agree to let the money follow students to schools of their choice.

In practice, this would mean a giant influx of federal money into private schools, which would be tied to students. So if a student chose to attend a public school, the public school would get the money; if she went to a private school, the private school would benefit.

It’s not clear if Congress will go along with this plan. Some Republican members of Congress have wanted a similar arrangement for years. But Congress also just passed a major education law, the Every Student Succeeds Act, and Democrats would strongly resist any attempt to turn federal school funding into vouchers.

DeVos will be hamstrung as education secretary

If Congress doesn’t pass Trump’s vouchers plan, the Education Department’s main role in K-12 education is approving plans for states to hold their schools accountable. DeVos has supported some state accountability ideas, like grading schools on an A-to-F scale based on test results, that could guide her actions here.

Otherwise, the Every Student Succeeds Act severely curtails the education secretary’s other powers. After Duncan used grant programs to push states to adopt Common Core standards and change the ways they evaluate teachers, the law strictly forbids future education secretaries from that kind of meddling.

But the education secretary will also oversee higher education, an area where DeVos has no expertise or history of activism — including overseeing the $127 billion annual federal student loans and Pell Grants program. Trump had proposed changing student loan repayment plans, and the next education secretary could also oversee a rewriting of the Higher Education Act, the law governing federal student loan and grant programs that is periodically renewed.

It’s not clear how much interest DeVos has in these issues. By choosing a single-issue activist as his education secretary, Trump suggests he’ll have a single-issue Education Department — but even putting his plans for that issue into motion will require consent that Congress isn’t certain to give.