A man walks past health insurer Anthem's corporate headquarters in Indianapolis in 2015. (Michael Conroy/Associated Press)

ANOTHER WEEK, another insurance company deserting patients in a wide swath of the country. Last Tuesday, Anthem announced it would pull out of the Obamacare marketplace in Ohio, potentially leaving individual insurance-buyers in about a fifth of the state’s counties without Affordable Care Act coverage to purchase. The news came after insurers in various other states announced or threatened market exits or big rate hikes over the past several weeks.

Are these moves more evidence that Obamacare is fundamentally unworkable? Hardly. Of greedy insurance companies callously disregarding their customers’ health? Not that either. Anthem explained clearly what is responsible for its retreat: Republican sabotage of the health-care system.

The Trump administration has been serially unclear about whether it will keep funding a crucial subsidy program, known as cost-sharing reductions . Without them, insurers would have to jack up premiums to cover their costs or leave markets that would become deeply unprofitable to them. Just as experts and industry officials predicted, insurance companies have done both as the uncertainty about these subsidies has grown.

Key Republicans understand the damage they are doing. “Insurers have made clear the lack of certainty is causing 2018 proposed premiums to rise significantly,” House Ways and Means Committee Chairman Kevin Brady (R-Tex.) said Thursday, arguing that Congress should step in. As the administration still appears determined to stoke uncertainty, lawmakers would have to move quickly to prevent more damage.

The question of cost-sharing reductions is only the biggest of many fears the Trump administration is inspiring. The president’s maladministration could include lax enforcement of the individual mandate to purchase health insurance, inadequate efforts to enroll more people in coverage and other gratuitous subversions of the finely tuned system Obamacare sought to create.

The GOP, however, still seems more motivated to solve a problem that does not exist — saving a health-care system supposedly on the path to inevitable collapse by repealing and replacing Obamacare. Senate Majority Leader Mitch McConnell (R-Ky.) is reportedly determined to vote soon on an Obamacare repeal-and-replace bill, getting the issue off the agenda ahead of the summer. The senators piecing together the language appear to be moderating the bill the House passed last month, and they could have a draft soon as they work toward a vote in coming weeks.

It is good news that senators may make their bill more centrist rather than, as the House did, more austere in order to pass it. But repeal-and-replace is unnecessary and, even in a more moderate form, risks doing great harm. Rolling back Medicaid, no matter when it is done, could result in many near-poor people losing coverage. Skimping on subsidies that help people buy insurance and loosening certain coverage regulations could hike deductibles and price poorer and older people out of the market.

Meanwhile, if the Senate fails to pass a bill but the GOP’s Obamacare sabotage continues, the health-care system would develop large coverage holes and face the risk of enrollment declines after years of progress expanding coverage.

Polls show Americans would prefer that the existing system be fixed.