The Patient Protection and Affordable Care Act was passed by both chambers of Congress and signed by President Barack Obama in 2010. It was upheld as constitutional by the U.S. Supreme Court in 2012.

But that’s not stopping some grandstanding South Carolina legislators from proposing to nullify it on constitutional grounds.

That exercise in futility is touring the state this week during public meetings on the S.C. House’s “Freedom of Health Care Protection Act,” including one from 6 to 8 p.m. today in council chambers at North Charleston City Hall.

The legislation would forbid any state agency, officer or employee from aiding “the enforcement of those provisions” of Obamacare “that exceed the authority of the United States Constitution.”

Hmm. By what authority will S.C. legislators overrule the U.S. Supreme Court ruling that deemed the law constitutional?

Yes, Obamacare passed without a single Republican vote and is plainly unaffordable for a nation already facing overwhelming entitlement costs. The high court’s decision upholding it was convoluted. And some scholars still argue that the states retain some nullification rights under the 10th Amendment.

Arcane debates about 18th century constitutional intent, however, can’t trump this 21st century reality:

Any real chance of repealing, or even significantly reforming, Obamacare lies not in state legislatures or federal courts but in the U.S. Congress.

Last year’s Supreme Court ruling did at least overrule the law’s requirement that states participate in the expansion of Medicaid to everyone below 138 percent of the federal poverty level. That gives the states the option to accept or reject it.

The pitch for joining the expansion is that Washington will cover all of the extra costs for the first three years, then 90 percent of them until 2022.

Then what?

In light of that troubling question, 24 states have not signed onto expansion. That includes our state, where Gov. Nikki Haley is rightly wary about expansion’s potentially crushing long-term obligation on taxpayers.

And before buying the Obama administration’s assurances on federal Medicaid money, review the spreading shock in some naive quarters over this already-broken vow from the president: “If you like your health-care plan, you’ll be able to keep your health-care plan.”

President Obama frequently reprised that pledge when pushing the law through Congress. The bill’s opponents correctly warned that it was a promise the law wouldn’t keep.

So we share the skepticism about guarantees of federal contributions to future Medicaid expenses.

Yet we also share S.C. Health and Human Services Secretary Tony Keck’s concerns that a General Assembly bill nullifying Obamacare, if passed, would endanger the state’s ability to keep receiving any federal Medicaid funding.

As for the president’s increasingly embarrassing efforts to explain away his broken promise, marvel at the immense gall he summoned for this silly spin during a speech to supporters Monday:

“If you have or had one of these plans before the Affordable Care Act came into law and you really liked that plan, what we said was you could keep it if it hasn’t changed since the law’s passed.”

That’s an absurd dodge unworthy of Mr. Obama’s high office.

But trying to nullify Obamacare is an absurd waste of our state lawmakers’ time.