"Medicare for All” is already a flashpoint in the 2020 presidential campaign. But as big as this fight will be, an even bigger issue lurks in its shadow. The health insurance that Americans pay for and receive is a function of where they live, and that could become even more true in the months and years ahead.

Shortly before Inauguration Day in 2017, President Trump tweeted out a warning: “People must remember that Obamacare just doesn’t work, and it is not affordable -- 116 percent increases.” He was talking about Arizona.

His claim was true only in part. The figure Trump quoted was the increase for a 27-year-old in a mid-range “silver” plan. But it wasn’t the case all over the state. Blue Cross Blue Shield of Arizona increased its rates by 51 percent, not a small number, but nothing like 116. In the Phoenix area, rates offered by Ambetter, another insurance company, increased 74.5 percent.

The next year proved to be an entirely different story. The cost of a silver plan for a 27-year-old Arizonan increased just by one dollar, and the overall cost in the state was very close to the national average. Moreover, the increases there weren’t ones that most people actually paid, because federal subsidies covered the bulk of the cost.

These issues are so arcane that engaging in a serious debate is difficult for anyone but a sophisticated health-care economist. Almost half of all Americans, a poll by the Kaiser Family Foundation found, do not know the difference between Medicare’s coverage for the elderly and Medicaid’s support for the poor. When asked about Medicare for All, three-fourths of Americans like the idea of allowing people to buy health insurance through Medicare or Medicaid, but their support plummets when they hear some of the arguments against it.

Assertions both for and against broader care are abundant right now, on all sides of the ideological spectrum. Broadsides that fit into 280-character Twitter feeds are handy for politicians and especially for candidates. But when these claims collide with the staggering intricacy of managing the health insurance system, the rhetoric melts in the heat of mind-numbing complexity.

In Arizona, the big premium swings in the last couple of years came largely from mistakes by insurers. Some companies low-balled their prices to gain market share. They signed up lots of people only to see their customers’ needs end up far greater than expected. That jolted rates upward and drove some of those companies out of business. Some new insurers jumped in to snap up the business and suffered the same fate.

This scared many insurers out of the game, and in some parts of the state, such as Pinal County in suburban Phoenix, no insurers wanted to write policies at all. Only one of the state’s counties, Pima, ended up with more than one insurer for 2017, and that essentially meant no competition for prices. The state’s insurance markets eventually stabilized, but only after Arizona had become a poster child for Obamacare gone wrong. Experts in the field reminded critics that it took years, and several rounds of administrative amendment, to get the Social Security program right. But few have been listening to those cautionary notes.

There are big price differences from one place to the next. Consider Minneapolis and Milwaukee, which have similar populations, similar hospital systems and similar health-care costs. In 2019, Affordable Care Act (ACA) premiums for a silver plan in Milwaukee are $563, compared with $300 in Minneapolis. Rates in Minneapolis fell 8 percent in the past year, while they stayed about the same in Milwaukee. 

Those differences might seem surprising. But Minnesota expanded Medicaid coverage as part of the ACA, and Wisconsin did not. States such as Minnesota that have taken part in Medicaid expansion have tended to have lower premiums, and more of the uninsured have been brought into the health-care system. In Wisconsin, the failure to expand Medicaid has meant higher costs for state government.

That’s resulted in a befuddling tug-of-war over who has it right, and only two things are certain. One is that how much individuals pay depends on their place of residence. The other is that this system is so complicated, and so decentralized, that educating the public is almost impossible.

As a result, partisans retreat to their corners and fling tweets at each other. Liberals call for a bigger federal role in providing health care. When confronted with what that would mean, many voters blanch. Conservatives call the liberals’ plans a strategy for socialism, and they favor pushing government out of the health-care business. But with health-care costs accounting for more than one-fourth of the federal budget, that’s not an option.

This is shaping up to be a pivotal -- and nasty -- debate for the 2020 campaign. It’s a difficult issue to debate, though, because we’ve made it so complex. And it’s so complex because for a long time the feds have found it easier to push tough decisions down to the states. That’s why the health care citizens get increasingly depends on their address. For an issue as fundamental as health care, those differences are a prescription for tearing even deeper rifts in the country.