The 2018 session of the Virginia General Assembly came to an end Saturday. But as the final gavel came down, one issue has yet to be resolved. And it’s a big one—perhaps the biggest job any state legislature has—approving a budget.

The stumbling block? Whether or not to expand Medicaid and accept the federal dollars that would accompany it.

The Affordable Care Act, also known as Obamacare, gives states the option of expanding Medicaid eligibility to people earning up to 138 percent of the federal poverty line. Barring any changes, the federal government has committed to picking up the entire tab for new enrollees during the next three years and will pay 90 percent of the cost down the road.

At present, 32 states and the District of Columbia have opted for Medicaid expansion. Eighteen—including Virginia—have not.

The House of Delegates’ version of the budget includes Medicaid expansion, which would provide health care to as many as 400,000 uninsur...