The problem is that the Republican plans eliminate the ACA’s requirement that all insurance policies provide robust minimum benefits like hospitalization and maternity care. Under a continuous-coverage system, that means healthy people could buy inexpensive skeleton plans and only shift to more inclusive coverage when they get sick, knowing that insurers must sell it to them. Christine Eibner, a senior Rand Corporation economist, said that scenario may prevent insurers from offering comprehensive plans to anyone on the individual market, because the only people buying them would be those with greater health needs. “You have a significant risk that this [entire] insurance market becomes bare bones,” she said.

That risk is compounded by another key GOP proposal: allowing any insurance policy approved in one state to be sold in any state. The ACA already allows interstate sale when all the affected states agree. But no insurer or state has pursued such cross-border sales, largely because out-of-state companies can’t easily compete with local insurers in building an affordable network of doctors and hospitals.

By eliminating minimum benefit requirements, though, the GOP proposals change the equation. The GOP plans would allow an insurer from a lightly regulated state to offer a low-benefit, low-cost plan that peels away younger and healthier consumers in states that require more complete coverage. If only those with greater health needs were left to buy the comprehensive coverage in more regulated states, medical costs would skyrocket—again raising the risk that no insurer would even sell such comprehensive coverage.