The Senate’s tax bill would eliminate the ACA’s penalty for being uninsured, starting on Jan. 1, 2019. That might seem like a long way away, but it’s not.

Insurers will start deciding this coming spring whether they want to participate in the exchanges in 2019 — and if so, where. Without the mandate, insurers would likely begin to pull back from state marketplaces early next year, likely leaving many parts of the country with no insurance plans to choose from.

Insurers will then have to finalize their 2019 premiums next fall. Those rates would likely be substantially higher (10% higher, on average, according to the Congressional Budget Office) without the mandate in place — and that news would hit just before next year’s midterms.