Political uncertainty isn’t the only threat to the Affordable Care Act’s future. Cracks also are spreading through a major pillar supporting the law

Health insurance exchanges created to help millions of people find coverage are turning into money-losing ventures for many insurers.

The nation’s largest, UnitedHealth Group Inc., could lose as much as $475 million on its exchange business this year and may not participate in 2017. Another major insurer, Aetna, has questioned the viability of the exchanges. And a dozen nonprofit insurance cooperatives created by the law have already closed, forcing around 750,000 people to find new plans.

More insurer defections would lead to fewer coverage choices on the exchanges and could eventually undermine the law, provided the next president wants to keep it.

Transitional Reinsurance is a key part of the Affordable Care Act. It’s a component of a set of provisions designed to lure private health insurers into selling insurance on various Exchanges. Without continued private insurer participation, Obamacare as we know it falls apart. Congress thought it needed lures (1) because health insurers did not have much experience with the medical expenses of the population they would be insuring and (2) because Congress was outlawing health insurers’ favorite technique for staying profitable: pricing policies according to the predicted medical expenses of the insured. Congress set the hook by giving insurers selling on the Exchanges something for free that they otherwise would have to pay for: reinsurance. With “Transitional Reinsurance” The federal government would itself pick up the bill three years for much of the expense of insureds who ended up having high medical expenses.

But, as with lunch, there is really no such thing as free reinsurance.

Donald Trump had a complete meltdown Thursday night when he got locked in this exchange with Marco Rubio over health care. Rubio kept pressing him on what his plan for health care was, and Trump responded by incoherently talking about getting rid of “the lines around the states.” Essentially, Trump wants to increase competition by allowing insurers to sell plans across state lines without regard to the states’s own insurance regulations.

Setting aside the fact that Trump’s understanding of health care policy is woefully inadequate, his one idea on health care isn’t even a good one. Granted, this is an idea a lot of Republicans have floated and, in theory, increased insurance competition is needed and state insurance regulations are often an impediment to this. But in practice, the idea runs into the buzzsaw of federalism.

The recent lawsuit filed by the Health Republic Insurance Company of Oregon regarding ObamaCare’s “risk corridor” program raises the question: Does the federal government have a duty to defend the lawsuit? Could they confess that the plaintiffs are right, or, better still, settle the case for the face value? Nicholas Bagley of the University Of Michigan School Of Law does not think the feds will do that while they can still argue that the claims are unripe. But if the case gets past the initial procedural hurdles, they’ll be sorely tempted to cut a deal.

Highmark Health is cutting reimbursement to doctors by 4 percent effective April 1 for care provided to patients with health insurance bought through the government exchange — the latest effort to trim losses in a market segment that has caused headaches for carriers nationwide.

All Pennsylvania doctors who participate in Highmark’s health insurance plans and treat patients with coverage required by the Affordable Care Act will be affected by the reimbursement cut, said Alexis Miller, senior vice president of individual and small group markets.

The doctors’ pay cut is needed to stem losses in individual health-law coverage as the insurer looks for other ways to stop the bleeding, Ms. Miller said.

According to the Kaiser Family Foundation (KFF), average premiums in the workplace were up 24 percent for individual plans and 27 percent for family plans. The vast majority of privately insured Americans – 9 out of 10 – purchase coverage through their employers.

Cost-sharing grew even faster. KFF reports that the average deductible for all workers was $1,077 in 2015, up from $646 in 2010—a 67 percent increase.

Over the past 5 years, a typical family of four faced 43 percent higher health costs, including both premiums and out-of-pocket expenses.  The Milliman Medical Index also shows that employer costs increased by 32 percent, from $10,744 in 2010 to $14,198 in 2015.  That’s nearly $3,500 that could have gone into paychecks if health costs had not soared.

California’s health exchange may require its health plans to pay sales commissions to insurance agents to keep insurers from shunning the sickest and costliest patients.

Covered California is working on a proposal that would force the plans to pay commissions effective next year, said Executive Director Peter Lee. The proposed rules could apply to regular and special enrollment periods, and would leave the specific commission amount or percentage up to insurers, he said.

Regulators in other states have warned insurers about altering commissions in a way that discriminates against higher-cost consumers, but Lee said Covered California may be the first exchange to adopt specific rules.

Hundreds of thousands of people lose subsidies under the health law, or even their policies, when they get tangled in a web of paperwork problems involving income, citizenship and taxes. Some are dealing with serious illnesses like cancer. Advocates fear the problems, if left unresolved, could undermine the nation’s historic gains in health insurance.

Coverage disruptions due to complex paperwork requirements seem commonplace in the health law’s system of subsidized private insurance, which currently covers about 12.7 million people.

The government says about 470,000 people had coverage terminated through Sept. 30 last year because of unresolved documentation issues involving citizenship and immigration. During the same time, more than 1 million households had their financial assistance “adjusted” because of income discrepancies. Advocates say “adjusted” usually means the subsidies get eliminated.

After most health insurers racked up financial losses on Affordable Care Act plans in 2014, many companies’ results for last year worsened, creating heavy pressure to improve performance this year.

An analysis of filings by not-for-profit Blue Cross and Blue Shield insurers—among the biggest players in the law’s exchanges for buying individual insurance—shows the challenge facing the industry as it seeks a turnaround in the individual business. They paid out more for health care in the first three quarters of 2015 than they took in from premiums on their individual plans.

On Wednesday, Humana Inc. became the latest of the big publicly traded companies to flag problems, saying its losses on individual plans deepened last year. Humana included in its 2015 results $176 million in losses it expects to incur on such plans in 2016.

Democratic candidate Bernie Sanders recently released his health-care plan: a government-run single-payer system for the U.S., similar to what many European countries have. Criticism of the plan has so far focused on its lack of political feasibility, but there is an even more important reason to be wary: Accounting for costs and tax increases, it would reduce labor supply by 11.6 million. In a struggling economy, with tepid wage growth, hurting employment should be the last thing on any politician’s agenda.

The plan truly promises everything under the sun. Not only will everyone be able to get any medical treatment needed — with no cost at the point of service — but the plan won’t require a terribly high tax increase.