The fate of the nation’s most ambitious school choice program is up in the air following the narrow election of Democrat Katie Hobbs as Arizona’s governor.

The state’s Empowerment Savings Account program is the first universal education savings account program in the country. Its opponents are already maneuvering to try to stifle the program by capping its size — and are hoping Ms. Hobbs will work with the legislature to do so.

Ms. Hobbs vigorously opposes the program, which gives families in Arizona whose children do not attend public schools $6,000 of taxpayers’ money per child per year to be spent on the educational expenses of their choosing. The sum is roughly equivalent to what the state pays per-capita in its public schools.

Currently, there is no cap on the number of students enrolled in the program — making it universally available to any student seeking to join.

Over the summer, the outgoing Republican governor, Douglas Ducey, signed into law a bill that made the education saving accounts available to every student — eliminating eligibility requirements. In a recent radio interview, Mr. Ducey touted the program as his proudest achievement in office.

“I think not only can this reform K-12 education, I think this can renew our nation,” Mr. Ducey said. “We’re the gold standard for educational freedom.”

The program has won broad acclaim from school choice advocates across the country — including an award from Jeb Bush’s education reform foundation, ExcelinEd. Supporters hope it will be a model for other states. 

In August, school choice advocate Corey DeAngelis called the program’s expansion “the biggest school choice victory — not just in Arizona — but in U.S. history.”

The expansion of the program came on the heels of a growing “parents rights” movement across the country demanding greater autonomy in their children’s education. Moms for Liberty and Parents Defending Education emerged to advocate for greater parental involvement in public school education.

The incoming governor, however, views increasing school choice offerings as anathema to the success of public education. In 2011, when Ms. Hobbs was a state senator, she voted against a bill that created an earlier version of the program — back then reserved only for students with disabilities. 

During her campaign for governor, Ms. Hobbs made clear that her position hasn’t changed in the past 11 years. In a recent PBS interview, Ms. Hobbs said she would not have signed the expansion bill codified over the summer.

“This voucher system we are under now doesn’t provide real choice in educational opportunity for most families,” Ms. Hobbs said. “It diverts resources from public schools and provides a subsidy for already wealthy children whose parents could already afford private education for them.”

Despite Ms. Hobbs’s opposition, however, the program will remain in place because of a Republican majority in the state legislature. Yet its defining feature — the universality and flexibility — could come under fire. More than 30,000 students have enrolled in the program since the expansion this fall.

“We really want to introduce accountability and transparency in the program so that voters at least know where their money goes,” the director of a public school advocacy group, Beth Lewis, says. “We’re talking $245 million, and that money is not accounted for. There’s no budget item for that.”

Ms. Lewis’s organization, Save Our Schools, tried to halt the program with a ballot referendum that ultimately failed to garner enough signatures to get on the general ballot. Its political action committee has received more than $100,000 in funding from the Invest in Arizona PAC, which is financed heavily by the state’s teachers union.

Because the program is universal, it is not bounded by a total budget. Rather, as students enroll in the program, its budget expands per capita. Ms. Lewis, herself a public school teacher, and public school advocates want to see the state designate a specific line in the budget for the program independent of other funding for public schools.

“If vouchers were a separate line item, if there was a cap — all of those are going to make sure that taxpayer money is not completely squandered at the expense of public schools,” Ms. Lewis told the Sun. “You can’t just shrug and say, ‘I don’t know how many people will take the voucher so we’re not going to allocate any funding to it.’ I think that’s just irresponsible.”

Setting a budget amount would effectively limit the number of savings accounts available — putting an end to the universality of the program.

“We need to put some guardrails on this program to make sure that private school operators are not able to just walk away with taxpayer dollars because, unfortunately, we’re definitely gonna see that happen,” Ms. Lewis said.

In tandem with the passage of the program, which diverts an estimated $250 million from public schools, the legislature increased public school funding by $600 million, according to a conservative think tank, the Goldwater Institute.

A prominent school choice activist in Arizona, Matthew Ladner, said his colleagues are approaching a Hobbs governorship with “a weary feeling of cautious optimism.”

“In a lot of ways, we’ve been through this before, back when Janet Napolitano was elected governor,” Mr. Ladner, the director of the Arizona Center for Student Opportunity, told the Sun. “No one knew how exactly that was going to work out, but it actually turned out to be a very productive period in terms of policy reform, including school choice.”

Under the Democratic Ms. Napolitano, the Republican legislature expanded school choice offerings through voucher laws and corporate tax credits. Ms. Napolitano signed the bills, making her the first Democratic governor in America to sign a school voucher bill into law.

Mr. Ladner hopes Ms. Napolitano’s term can serve as a precedent for the Republican legislature to pass a school-choice-friendly agenda with the signature of a Democratic governor.

Arizona’s current school choice policies extend far beyond just the savings account program. A fifth of Arizona students attend charter schools. Even public school students are not limited to their local schools. The state’s open enrollment policies allow students to attend higher-performing public schools if there is room for them.

In the Phoenix metropolitan area, for example, fewer than half of students attend their neighborhood public schools — with large numbers of students choosing to enroll in other public school districts, charter schools, or private schools.

“It’s always possible for the legislature to pass legislation to change any and all of these things, but whether or not any kind of consensus will develop remains to be seen,” Mr. Ladner said.

Ms. Hobbs’s office did not respond to a request for comment.