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 saying that it will completely divorce itself from state-based insurance exchanges.

Aetna says it won’t sell individual coverage in Nebraska and Delaware next year after projecting a $200 million loss this year. The insurer had already pulled out of several states after losing about $450 million in 2016.

The exchanges are a pillar of the federal law because they allow millions of people to buy coverage with help from income-based tax credits. But insurers like Humana, and now Aetna, have been fleeing that market. Others like the Blue Cross-Blue Shield carrier Anthem say they are wary of returning without guarantees of at least one key financial support.

Every exchange had at least one insurer offering coverage for 2017, but a growing number were down to only one. Insurance experts expect holes to develop in 2018 with the coverage growing so thin. Customers may be able to find individual insurance coverage off the exchanges, but those marketplaces offer the only way for people to get tax credits to help pay the premium.

About 12 million people bought coverage through the exchanges for this year. Most used tax credits to help buy coverage.