Christopher Robertson is a professor of law and the associate dean for research and innovation at the University of Arizona. He is author of the new book, Exposed: Why Our Health Insurance is Incomplete and What Can be Done About It (Harvard University Press, 2019). The views expressed in this commentary belong to the author. View more opinion at CNN.

(CNN) Polls show that health care is the single most important issue for voters, so it is not surprising that Democratic candidates have been busy releasing policy proposals. But too much of the focus has been on who gets covered and not enough on the quality of coverage and the rising cost of health care, which many voters said was what mattered the most when asked why health care was so important.

Much of the current health care debate and likely what we might hear when Democratic candidates debate in Iowa on Tuesday centers on whether we should abolish private insurance and move to "Medicare for All," with differing strategies to pay for it. And should we extend coverage to undocumented immigrants , or low-income citizens who are not working?

But answering those questions does little to help the three in 10 adults who, according to a 2019 KFF health tracking poll, reported that costs caused them not to take their medicines as prescribed.

More than 90% of Americans already have health insurance, and the past 30 years have seen increased copays, deductibles and co-insurance. Deductibles, for example, have grown 212% in the last decade alone, which is about 12 times more than the rate of inflation and eight times more the rate of wages.

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In my research with people going through foreclosures at the height of the crisis in 2008, I found that most of the homeowners were actually facing expensive medical problems. It's hard to earn wages to pay your mortgage when you are flat on your back in a hospital, and if you have any financial reserves at all, they can be wiped out the moment the ambulance arrives. And our research found that medical problems drove foreclosures, regardless of whether patients had health insurance. American health insurance provides incomplete coverage, leaving families exposed to devastating levels of risk in the forms of copays and deductibles. Even under Obamacare's insurance regulations, companies can still impose up to $16,300 in copays per year.

Serious healthcare reform would eliminate substantial copays, deductibles, and co-insurance, and instead make insurance coverage complete. It is perhaps unsurprising that Bernie Sanders has proposed exactly that, and Elizabeth Warren has too. But they are taking lots of heat from moderates, who frame the reforms as too radical. Regardless of that debate, it's clear that in their repeal of cost-exposure, Warren and Sanders are addressing the key questions of quality coverage and affordability that Americans are concerned about.

Trump has also acknowledged the problems with growing health care costs. In January 2017, as he was preparing his move to the White House, he told the Washington Post that TrumpCare would have "much lower deductibles." And the ability to pay, he said, wouldn't be an issue. "There was a philosophy in some circles that if you can't pay for it, you don't get it. That's not going to happen with us." Of course, Republicans have instead merely tried to chip away at the ACA protections, and they have done nothing to really lower deductibles.

Nonetheless, Trump's first Food and Drug Commissioner Scott Gottlieb similarly said , "Patients shouldn't be penalized by their biology if they need a drug that isn't on formulary. Patients shouldn't face exorbitant out of pocket costs ... sick people aren't supposed to be subsidizing the healthy."

It is striking to hear such words from Republicans, even while out-of-pocket costs continue to skyrocket. Yet it is a misnomer to call copays and deductibles "out of pocket costs," since Americans generally don't have cash for heart stent surgeries or chemotherapy drugs, in their pockets or anywhere. Instead, if people are able to get healthcare at all, they are financing our healthcare system with consumer debt. And it's just not sustainable. According to a 2019 Gallup survey, Americans borrowed a total of $88 billion to cover health costs.

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Other countries have already proven that it need not be this way, according to a 2017 Commonwealth Fund report. In Canada, nearly 70% of health spending comes from public sources, and for physician, diagnostic, and hospital services covered by public insurance, there is no patient cost exposure whatsoever. Yet Canada manages to achieve significantly less health spending overall—only 10.5% of its GDP compared to 17.2% in the United States, according to 2014 numbers from the report. Even less, New Zealand spent only 10.9% in 2014 on healthcare, yet patients spent only US$263 out of pocket, about one-quarter of the American exposure. Japan likewise spent only 11.4% of its GDP on healthcare in 2014, but uses monthly caps, income caps, age caps, and various waivers, so patients spent out of pocket only US$126 —about one-tenth of what Americans paid.

When citizens of each country were surveyed for the Commonwealth Fund report , only 19% of Americans say their healthcare system works well, compared to 35% in Canada and 41% in New Zealand.

These international examples show that, although Americans may assume that big copays and deductibles are a necessary part of any economical healthcare system, this is not true. Indeed, in these other countries the healthcare systems get along just fine, with performance metrics that are comparable, or better, than the US healthcare system.