Policymakers in some states that haven’t adopted health reform’s Medicaid expansion said they wanted to wait for the Supreme Court’s ruling in King v. Burwell before deciding whether to expand. With yesterday’s ruling, which ensures that consumers in states using the federal marketplace will continue receiving subsidies to buy health coverage, any pleas for more time ring hollow.

More than 16 million Americans have gained coverage due to health reform, and the best way to add to these historic coverage gains is for the remaining 21 states (see map) to expand Medicaid. That would provide access to health coverage to more than 3.7 million uninsured adults now caught in a “coverage gap,” with incomes too high for Medicaid but too low to qualify for federal subsidies to buy marketplace coverage.

Mounting evidence shows that expanding Medicaid has been the right decision for states:

While the uninsured rate has dropped to a historic low nationally, expansion states have experienced much larger gains than non-expansion states.

Expansion has produced net savings for state budgets. With more uninsured individuals obtaining coverage, states are spending less on health care services for low-income uninsured residents. States expect these savings to grow over time.

Hospitals in expansion states are treating fewer uninsured patients so they are providing less uncompensated care.

The Supreme Court decision means that health reform is here to stay. Policymakers in the 21 holdout states can best serve their residents by stepping up and quickly adopting the Medicaid expansion.