Opting into the Medicaid expansion means about 130,000 more people will enroll in the program.
The rate of growth in spending will accelerate starting in 2020 because of the smaller federal match.
Additionally, it's possible that the federal share could be reduced further as Washington tries to get spending under control.
With West Virginia's coal industry softening, Tomblin is trying to keep a tight rein on the budget. There's no new spending planned for next year, except for Medicaid and to keep retirement programs actuarially sound.
And Tomblin is cutting spending in some areas of government by 7.5 percent.
Politico reports that Sen. Jay Rockefeller, a long-time advocate of expanded government health care, is confident Tomblin will eventually come on board.
"I've stayed in close touch with the governor's office through this process, and I know they are working to understand the details," Rockefeller told Politico.
"I think at the end of the day, the numbers will show that expansion would greatly benefit West Virginians."
Perhaps, but for now Tomblin is keeping his cards close to the vest, while his budget people try to figure out how much all this is going to cost.
Kercheval is host of TalkLine, broadcast by the MetroNews Statewide Radio Network from 10 a.m. to noon Monday through Friday. The show can be heard locally on WCHS 580 AM.