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.

Some background: Obamacare rests on three pillars. First, insurers must offer the same coverage to everyone regardless of medical history. Second, everyone must purchase coverage — the famous “mandate” — so that the young and healthy don’t opt out until they get older and/or sicker. Third, premiums will be subsidized, so as to make insurance affordable for everyone. And this system is going into effect next year, whether Republicans like it or not.

Under this system, by the way, a few people — basically young, healthy individuals who don’t already get insurance from their employers, and whose incomes are high enough that they won’t benefit from subsidies — will end up paying more for insurance than they do now. Right-wingers are hyping this observation as if it were some kind of shocking surprise, when it was, in fact, well-known to everyone from the beginning of the debate. And, as far as anyone can tell, we’re talking about a small number of people who are, by definition, relatively well off.

Back to the Medicaid expansion. Obamacare, as I’ve just explained, relies on subsidies to make insurance affordable for lower-income Americans. But we already have a program, Medicaid, providing health coverage to very-low-income Americans, at a cost private insurers can’t match. So the Affordable Care Act, sensibly, relies on an expansion of Medicaid rather than the mandate-plus-subsidy arrangement to guarantee care to the poor and near-poor.

But Medicaid is a joint federal-state program, and the Supreme Court made it possible for states to opt out of the expansion. And it appears that a number of states will take advantage of that “opportunity.” What will that mean?A new study from the RAND Corporation, a nonpartisan research institution, examines the consequences if 14 states whose governors have declared their opposition to Medicaid expansion do, in fact, reject the expansion. The result, the study concluded, would be a huge financial hit: the rejectionist states would lose more than $8 billion a year in federal aid, and would also find themselves on the hook for roughly $1 billion more to cover the losses hospitals incur when treating the uninsured.

Meanwhile, Medicaid rejectionism will deny health coverage to roughly 3.6 million Americans, with essentially all of the victims living near or below the poverty line. And since past experience shows that Medicaid expansion is associated with significant declines in mortality, this would mean a lot of avoidable deaths: about 19,000 a year, the study estimated.

Just think about this for a minute. It’s one thing when politicians refuse to spend money helping the poor and vulnerable; that’s just business as usual. But here we have a case in which politicians are, in effect, spending large sums, in the form of rejected aid, not to help the poor but to hurt them.

And as I said, it doesn’t even make sense as cynical politics. If Obamacare works (which it will), millions of middle-income voters — the kind of people who might support either party in future elections — will see major benefits, even in rejectionist states. So rejectionism won’t discredit health reform. What it might do, however, is drive home to lower-income voters — many of them nonwhite — just how little the G.O.P. cares about their well-being, and reinforce the already strong Democratic advantage among Latinos, in particular.

Rationally, in other words, Republicans should accept defeat on health care, at least for now, and move on. Instead, however, their spitefulness appears to override all other considerations. And millions of Americans will pay the price.