It seems like a no-lose proposition for a politician: a promise to provide college for free. But as some Democratic presidential candidates make that pledge — and as a growing roster of states embrace the idea — the free college movement is highlighting economic and social tensions and exposing a divide on who should benefit from government aid.

Should it be restricted to those of limited means? Or should everyone benefit equally, even if it’s a student who has been raised amid privilege and goes on to become a high-earning doctor or a lawyer?

In the last year, Maryland and New Jersey have joined a host of states from Rhode Island to Oregon in enacting statewide scholarship programs that cover tuition at community colleges. Their legislatures span the ideological spectrum but have coalesced around the idea that an educated workforce could strengthen the local economy.

Other states, including Virginia, are considering similar scholarships. And in New York, the free tuition benefit extends to residents attending public four-year universities. Each program comes with eligibility criteria, including age, grade or employment restrictions.

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The question for some states, as for Democratic presidential candidates, is how many years of education are necessary and who deserves it for free.

Those questions took center stage in last month’s presidential debates. Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.) reiterated their support for the federal government picking up the tab for the cost of public two- and four-year colleges.

“I believe we must make public colleges and universities tuition-free and eliminate student debt, and we do that by placing a tax on Wall Street,” Sanders said.

Others vying for the Democratic nomination take a more targeted approach. Sen. Amy Klobuchar (Minn.) and former vice president Joe Biden say they would make community college free, while South Bend, Ind., Mayor Pete Buttigieg has advocated for free tuition for poor and middle-income students.

“I just don’t believe it makes sense for working-class families to subsidize tuition for billionaires,” Buttigieg said during the debate. “The children of the wealthiest of Americans can pay at least a little bit of tuition.”

Some higher education advocates say too many existing free college programs are structured in a way that does little to help people with the greatest financial need. Instead, the assistance should be targeted to students from low-income families, which, they say, would make the best use of limited resources.

Others argue the goal should be to make college affordable for most students. Many middle-income families are in no position to handle the full cost of higher education and are often shut out from need-based grants and scholarships. And while financial aid based on merit offers a lifeline to some families, it’s not nearly enough to cover high college costs for many students.

The proliferation of tuition-free community college programs offers lessons on enacting initiatives so that they withstand changing political agendas and economies. Some of the oldest state programs have survived budget cuts that could have threatened their sustainability. Others have managed to expand and place higher education within reach of more students.

“We want to maintain a steady course to grow these programs, learn from the best ones and then help replicate those that work,” said Martha Kanter, the executive director of the College Promise Campaign, which advocates making the first two years of college free. “It’s often a matter of having sound research to understand what works.”

A major sticking point among proponents of College Promise programs, as tuition-free initiatives are commonly known, is who benefits.

States that extend eligibility to families with higher household incomes tend to attract wealthier students more likely to be aware of their financial aid options, according to a study by the Century Foundation. The left-leaning think tank analyzed six statewide programs that thrived during the Great Recession and found some had greater staying power when they reached wealthier districts. A wider range of families, including the well-connected, helps gin up political support that often ensures longevity.

“A couple of the programs did bring in wealthier, politically influential students and families, but things like the early, almost contractual-like commitment to students, budget process protections . . . were features that helped drive continued investment in the programs,” said the Century Foundation’s Jen Mishory, who carried out the study.

Almost half of all dollars in Louisiana’s Taylor Opportunity Program for Students program — commonly known as TOPS — go to families earning more than $100,000, although the median income in the state is roughly half that amount, the study said. State lawmakers have touted the program as a middle-class benefit, making it easier to fight for funding.

The same is true in Missouri, where participation in its A+ scholarship skews toward students whose families earn far more than the state’s median income of about $60,000. The structure of the scholarship accounts for some of the disparity. Missouri has a last-dollar program, meaning the state covers tuition left over after factoring in federal and other state grants. As a result, low-income students who have enough financial need to qualify for federal Pell Grants receive the least amount of money.

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The last-dollar model is pervasive among Promise programs, including those in Maryland, New York and Tennessee. It allows states to stretch program dollars but also means there’s not money to help low-income students cover food, housing and other living expenses even after receiving federal aid.

A commitment of federal dollars may not make much of a difference when it comes to living expenses. Democratic candidates who back free college are focused on tuition, although several have called for the expansion of grant programs to address living costs. Few contenders have elaborated on how they would pay for their college proposals. Warren has proposed taxing the ultrawealthy to pay for her plan, while Sanders would impose a tax on transactions by hedge funds, investment houses and other Wall Street firms.

Lawmakers in some states insist it would be economically untenable for states to cover tuition upfront, rather than kick in whatever money is left over after a student’s federal grant aid is applied.

Still, some states have established first-dollar programs, with state money kicking in before federal aid, with restrictions. Oklahoma, which created its program in 1992, covers tuition before subtracting any grant aid a student receives. But the scholarship is restricted to students from families earning $55,000 a year or less.

While the Oregon Promise grant kicks in after federal and other state aid, the program awards the poorest students $1,000 for help with college books, fees and transportation if their tuition is already covered by federal grants.

Tuition-free community college plans that have emerged in the last few years share features that some student advocates find tone deaf or troubling.

Many are limited to full-time students or recent high school graduates, although nearly two-thirds of community college students attend part-time and one-third are age 25 and older, according to U.S. Education Department data.

Promise programs are designed to encourage timely college completion, which has led some states to require students to take 15 credits a semester to speed up graduation. But some community college students have children and work full-time, making a full course load difficult.

“You can utilize tools schools already have to make sure students are completing, like advising, instead of imposing restrictive enrollment criteria,” said Sara Garcia, a policy analyst at the Center for American Progress, a liberal think tank. “If you have a one-size-fits-all approach for all students, you’re going to miss out on students who can really benefit from these programs.”

Some states with established Promise programs are becoming more responsive to the needs of adults seeking higher education.

In Tennessee, lawmakers in 2017 expanded eligibility for the four-year-old Tennessee Promise from just recent high school graduates to adults who don’t already have an associate’s or bachelor’s degree. Advocates say an important feature of the new grant is that it is available to adults pursuing an associate degree part-time. The expansion will cost an estimated $10 million, which will come from the state’s lottery program, like the rest of the tuition program.

Indiana, Maine, Minnesota, Oklahoma and Washington are also developing pilot tuition-free programs for adult students with the help of the State Higher Education Executive Officers Association, a trade group.

But higher education experts worry that features in some of the newer Promise programs could prove counterproductive.

Maryland and New York, for instance, will turn their tuition grants into loans if recipients fail to work in-state for at least as many years as they received college assistance. New York Gov. Andrew M. Cuomo (D) has defended the residency requirement, saying the state should not pay to educate residents who move elsewhere after graduation.

“Everybody wants a quick answer, but this is going to take five to 10 years to get the metrics right, to engineer the eligibility criteria and . . . stabilize the funding stream,” said Kanter, a former undersecretary of education in the Obama administration. “There’s no easy solution because communities are different, the states are different, the politics are different and the money is different.”