House Republicans have voted 37 times to repeal ObamaRomneyCare — the Affordable Care Act, which creates a national health insurance system similar to the one Massachusetts has had since 2006. Nonetheless, almost all of the act will go fully into effect at the beginning of next year.

There is, however, one form of obstruction still available to the G.O.P. Last year’s Supreme Court decision upholding the law’s constitutionality also gave states the right to opt out of one piece of the plan, a federally financed expansion of Medicaid. Sure enough, a number of Republican-dominated states seem set to reject Medicaid expansion, at least at first.

And why would they do this? They won’t save money. On the contrary, they will hurt their own budgets and damage their own economies. Nor will Medicaid rejectionism serve any clear political purpose. As I’ll explain later, it will probably hurt Republicans for years to come.

No, the only way to understand the refusal to expand Medicaid is as an act of sheer spite. And the cost of that spite won’t just come in the form of lost dollars; it will also come in the form of gratuitous hardship for some of our most vulnerable citizens.