“This is a major initiative that will revolutionise higher education in this country and improve the lives of so many of our people.” So said Bernie Sanders of Hillary Clinton’s plan for “debt-free” public higher education, in the July speech in which he endorsed his former rival for the Democratic presidential nomination.

One of Mr Sanders' attention-grabbing pledges, highly popular with his supporters, had been to abolish tuition fees in public higher education and make it free for all. Ms Clinton’s on college stated that students should not have to borrow to pay for tuition, books or fees, but would have required families to make “an affordable and realistic family contribution”.

However, in July she went further and committed to a plan that would mean by 2021 students from families with income up to $125,000 (£95,000) will at in-state four-year public colleges and universities, a pledge covering 80 per cent of US families, according to her campaign.

Supporters of the plan will say that in the world’s most important, and most marketised, higher education system, it could mark an important shift towards seeing higher education as a public good accessible to all.

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Ms Clinton’s revamping of her policy was seen as an attempt to win backing from Mr Sanders and his supporters. But the political move brings important policy questions: whether this is the right remedy on college affordability and whether it has any chance of being implemented by a Clinton White House.

“During the primaries and in the debates, the main distinction that Clinton drew between her [original] plan and the Sanders plan was that the Sanders plan would pay for higher education for a lot of people who didn’t need help,” said William Doyle, associate professor of public policy and higher education at Vanderbilt University, a lead author on the 2016 ,��which found that affordability had declined in all 50 states since 2008.

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He added that it “does appear that Clinton’s new plan will spend a lot of money on students who would have gone to college without additional help – the same critique she levelled at Sanders”.��

Professor Doyle said that private institutions, not included in the plan, are “not necessarily elite or selective institutions” and often “play a big role in ensuring college access”.

He added: “There’s a real question of whether there’s an adequate supply of public college spots to enrol all of the students who are supposed to go tuition free.”��

The Clinton plan would provide federal grants to states to help remove tuition fees. But the plan would rely on state governments buying in and making a contribution.

The plan would be “fully paid for by limiting certain tax expenditures for high-income taxpayers”, the Clinton campaign has said.��Her aides have stated an estimated cost of $500 billion over 10 years, according to media reports.

Iris Palmer, a senior education policy analyst at the thinktank New America, said that there was a question over whether the costs of the programme could result in entry requirements at public colleges being toughened to limit numbers, a result that “ends up benefitting wealthy individuals”. There should be “low income enrolment targets” to counteract this, she suggested.

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If Ms Clinton does win November’s presidential election (she leads Republican nominee Donald Trump in the polls), she would also have to get her college plans through Congress.

The Republicans currently have a majority in both houses, although House of Representatives and Senate elections will also be held in November.

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Ms Palmer suggested that to pass the debt-free college plans through Congress, Ms Clinton would need “a filibuster-proof majority” of the kind enjoyed by President Obama in his first term.

“Getting something of this magnitude passed…would be very, very challenging,” she said, adding that to do so Ms Clinton might have to make debt-free college a “political priority” in the way President Obama made the Affordable Care Act a priority in his first term.

Ms Palmer also said the plan would be “building on top of the current system we have”, contrasting this with the “more radical” proposals in New America’s 2016 report, which called for a new federal-state relationship in higher education to replace the “irreparably broken” current system.

Professor Doyle said that most policy efforts on college affordability “have focused on ‘feeding the beast’, trying to provide money to keep up with tuition increases”.

“The price of higher education is being driven up by two factors: institutions keep getting more expensive to run every year, and states haven’t been able to keep funding the increasing expense of higher education,” he continued.

One big question for the Clinton plan, Professor Doyle said, is how it “will keep institutions from continuing to increase costs, and therefore prices, making this an expensive plan over the long term”.

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“While institutions have been getting more expensive to operate, they don’t have to be as expensive as they are – there have to be more efficient ways of running these institutions.” Any big plan on college affordability must “push on institutions to ‘bend the cost curve’ in order for it to be sustainable over the long term”, he added.

john.morgan@tesglobal.com