Earlier this year, Hillary Clinton brushed off a proposal for free public college tuition from her primary opponent Bernie Sanders with a zinger: "My late father said, 'if somebody promises you something for free, read the fine print.'"

Now, Clinton has adopted key planks of the Sanders plan, and she may be struggling with some of the fine print herself. On Monday, her campaign released a "college calculator" tool on her site that allows students to determine how much they would save under her plan. It's the campaign's first time pushing the plan since she announced her shift in July.

While Clinton's plan isn't the universal project Sanders outlined, she took a big step in his direction by proposing to cover public college tuition for families making up to $85,000, and by 2021, families making up to $125,000.

"[I]t is imperative that the next president put forward a bold plan to make debt-free college available to all," read statement announcing the plan. "My New College Compact will do just that—by making sure that working families can send a child or loved one to college tuition-free and by giving student debt-holders immediate relief."

So Clinton went from backing lighter "debt-free" college remedies to a more straightforward, Sanders-esque plan to pour money into public colleges and universities. Advocates hope this kind of policy will reinvigorate public education and turn colleges into the same widely public institutions as high schools. After all, free college is not a pie-in-the-sky, it used to work quite well in states like California.

But is Clinton's plan financially possible? Politically possible? Is it too much of a half-measure?

"The funding question is very simple, and I'll be very blunt," said Sara Goldrick-Rab, professor of higher education policy and sociology at Temple University. "We can absolutely afford to do this, and more."

Clinton has kept the funding details vague, with a reference to taxing the rich and closing loopholes for hedge funds, but Goldrick-Rab says it's not an issue anyway. "There is a ton of waste in the current system that the public is under-educated about, including a lot of money going to private companies like ITT, which just went under," she said. "And of course, education produces real returns on this kind of spending. It would pay off."

Robert Kelchen, assistant professor of higher education at Seton Hall University, is skeptical.

"This plan probably won't end up happening," he said. "The full plan is something over $500 billion over 10 years, and that's unlikely to pass Congress without filibuster-proof majority." There's also the danger that Republican governors won't play ball and reject partnering with the federal government, something Clinton herself mocked Sanders for during the primaries.

Kelchem also argued that the plan might backfire.

"The tuition-free part, that's something that could end up encouraging up more students to go to college–but it could also potentially squeeze lower-class out of public colleges," he said.

But Goldrick-Rab says that's based on a false assumption that capacity won't expand with all that available money. "There have been studies when a bond referendum is passed to fund community colleges, and they grow their capacity. Their capacity has been constrained by underfunding."

There are some recent examples of this: In 2005, University of California added UC Merced to its array of campuses because they needed to expand capacity. In Florida, a state that's slicing public education most times it can, still founded the public Florida Polytechnic University in 2012.

"People think that all these proposals do is lower the price, and they don't think about what's going in the back-end to further fund and expand and get you more room," Goldrick-Rab said.

Clinton's move, then, is certainly a step in the right direction for proponents like her, especially compared to the Republican ticket. Republican candidate Donald Trump is a blank slate on the issue, but his running mate Mike Pence has been on a crusade against public education funding even as he made use of $280,000 in federal Parent PLUS student loans to send his children to college.

Still, Sara Goldrick-Rab is not convinced Clinton is all in. "This calculator thing is too confusing, it isn't being pitched well. She needs a working class level outcry for it. What I can tell you is there is a community college in every district across this country, and if they could see something that could really help them, they would push for it."