FILE - In this Tuesday, Aug. 19, 2014, file photo, a pedestrian walks past a sign for Aetna Inc., at the company headquarters in Hartford, Conn. While Republicans rewrite the Affordable Care Act in Washington, the immediate future of the law has grown hazier with the nation's third-largest health insurer Aetna saying that it will completely divorce itself from state-based insurance exchanges. (AP Photo/Jessica Hill, File)

FILE - In this Tuesday, Aug. 19, 2014, file photo, a pedestrian walks past a sign for Aetna Inc., at the company headquarters in Hartford, Conn. While Republicans rewrite the Affordable Care Act in Washington, the immediate future of the law has grown hazier with the nation's third-largest health insurer Aetna saying that it will completely divorce itself from state-based insurance exchanges. (AP Photo/Jessica Hill, File)

While Republicans rewrite the Affordable Care Act in Washington, the future of the current law has grown hazier with the nation’s third-largest health insurer completely divorcing itself from state-based insurance markets.

Aetna said late Wednesday that it won’t sell individual coverage next year in its two remaining states — Nebraska and Delaware — after projecting a $200 million loss this year. It had already dropped Iowa and Virginia for next year. The insurer once sold the coverage in 15 states, but slashed that to four after losing about $450 million in 2016.

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The government-backed marketplaces are a pillar of the Obama-era federal law because they allow millions of people to buy health insurance with help from income-based tax credits. But insurers like Humana, and now Aetna, have been fleeing that market, and the remaining coverage options are growing thin. Other companies like the Blue Cross-Blue Shield insurer Anthem say they are wary of returning without a guarantee that the government will provide cost-sharing subsidies that reduce expenses like co-payments. Those are separate from the tax credits that help pay premiums.

The White House has assured lawmakers it will continue paying the subsidies, but it has offered no long-term guarantee.

About 12 million people bought coverage for this year on the exchanges, and every market had at least one insurer offering coverage. But a growing number were down to one.

Companies are in the middle of figuring out their prices and coverage plans for next year, and insurance experts expect some holes to develop in those marketplaces.

“All it takes is one insurance company to exit, and that can create panic for other insurers and they pull out too,” said Cynthia Cox, a health insurance expert for the nonprofit Kaiser Family Foundation, which studies health care. “Insurers don’t want to be the last one holding the bag.”

The federal law prevents insurers from rejecting patients based on their health, so if competitors pull out, the last insurer may be left covering all the high-cost patients in that market.

Metropolitan or highly populated areas are still expected to draw several insurers. But rural areas may not be attractive to insurers looking to cut losses. They generally have a smaller, older population.

Ultimately, insurers with the most common brand in health insurance, Blue Cross-Blue Shield, will decide the fate of the marketplaces. Many of those plans specialize in individual insurance and have a long-standing presence in their markets. They also are the only remaining option on exchanges in nearly a third of the nation’s more than 3,100 counties.