The latest Republican proposal to undo the Affordable Care Act would grant states much greater flexibility and all but guarantee much greater uncertainty for tens of millions of people.

The legislation, proposed by two Senate Republicans, Lindsey Graham of South Carolina and Bill Cassidy of Louisiana, would not only reduce the amount of federal funding for coverage over the next decade, but also give states wide latitude to determine whom to cover and how. The result is a law that would be as disruptive as many of the Republicans’ previous proposals, but whose precise impact is the hardest to predict.

The bill would initially preserve nearly all the funding currently provided to Americans through the Affordable Care Act’s state insurance marketplace subsidies and expansion of Medicaid. But starting in 2020, that funding would be reallocated to state governments as block grants. Over time, the division of money would shift among the states based on a complex formula, and the total pot would grow according to a set rate, not based on the number of people nationwide who sign up for coverage.

States could use the money to replicate the programs in President Barack Obama’s signature health law, or to pursue completely different health policy strategies. The bill lays out some standards for program goals, but gives states broad discretion to use the funds in a variety of ways. “There will be clear differences between states about how they implement,” said Deep Banerjee, an analyst with Standard & Poor’s. “It will create quite a bit of uncertainty over the next few years.”