Politicians have been lying since the dawn of the republic. Calling them out is an exercise in futility, roughly akin to handing out speeding tickets at the Indy 500.

But, every so often, a lie is so shamelessly brazen that it behooves us to bemoan it. Witness the Republican talking point du jour, about how President Obama has supposedly slapped a humongous tax hike on the middle class, thanks to his health-reform provision that requires most Americans to buy health coverage.

Ever since Chief Justice John Roberts upheld the law, writing that the noncompliance penalty was akin to a tax and that such taxes are constitutional, the GOP and its allies have been scaling new heights of hyperbole. The conservative Koch brothers bankrolled an ad calling it "one of the largest tax increases in American history." A Florida congressman upped the ante, calling it "the largest tax on the American people in history." Rush Limbaugh went further, calling it "the largest tax increase in the history of the world."

So far, nobody has called it "the biggest tax hike in the history of the whole universe whose origins can be traced to the subatomic particle known as the Higgs boson," but, hey, the election season is still young.

I know, politics ain't beanbag. Lies can help grease the path to victory. Two random examples: John F. Kennedy pumped up his anti-Soviet credentials in 1960 by inveighing against a "missile gap" that, in fact, did not exist. George H.W. Bush falsely depicted his 1988 opponent, Michael Dukakis, as a harbor-polluting, soft-on-crime wimp. That's often how the game is played.

But the GOP's new tax claim is in another league. So let's bridge the chasm between the lie and the truth:

Obama's supposedly sweeping tax — his penalty for noncompliance — will be levied on a grand total of 1.2 percent of the American people.

So says the nonpartisan Congressional Budget Office, in its projections for 2016. This means that 98.8 percent will not pay a cent, because virtually all Americans (a) will already have health coverage, (b) will have obtained coverage for the first time, thanks to federal subsidies and tax credits, or (c) will be exempt from the penalty, because of economic hardship or religious beliefs. The penalized 1.2 percent will be those Americans who can well afford coverage but simply refuse to buy it.

The CBO's 1.2 percent figure seems right on target, given what has happened in Massachusetts, home of the nation's first health-coverage mandate (and the model for Obamacare). The state law enacted in 2006 also features a noncompliance penalty; in fact, it's nearly double the size of Obama's penalty. But in 2009, less than 1 percent of the citizens had to pay it.

Defenders of the Massachusetts law have never characterized the mandate penalty as a massive tax on the middle class. They've insisted the penalty is merely the best way to punish the free riders who fob off their medical bills on other taxpayers. As one prominent defender said in 2006, "I don't think the free market ever envisioned an idea that people would be able to do something and make other people pay for it."

So said Gov. Mitt Romney.

It's most inconvenient for the Republicans to have a nominee who undercuts their new talking point. What they now falsely decry as a historically massive Obama "tax" is actually a narrowly targeted penalty that Romney pioneered.

Indeed, top Romney aide Eric Fehrnstrom said on TV Monday: "The governor has consistently described the mandate in Massachusetts as a penalty. ... The governor believes that what we put in place in Massachusetts was a penalty, and he disagrees with the [Supreme Court] ruling that the [Obamacare] mandate was a tax."

Hence the dilemma: How could the GOP inveigh against Obama's "tax" when its own nominee wouldn't call it a tax?

No problem, because the ever-changeable nominee has changed his mind. In a TV interview Wednesday, Romney threw Fehrnstrom under the bus. He contrived to Etch A Sketch his previous convictions and echo the party line about Obamacare. He said, "It's a tax."

I guess it's better for the Republicans to have Romney belatedly on board. But now they face a new dilemma: If the Obamacare mandate is a massive tax on the middle class, doesn't this mean that Romneycare mandate hiked taxes, too? From every angle, Romney is clearly a bad messenger for the big lie.

The lie has other components, by the way. When it falsely assails Obamacare as the largest tax hike in "American history," the GOP often cites not just the noncompliance penalty but the various fees that will be slapped on medical-device makers, pharmaceutical firms, tanning salons, and small-business owners who refuse to provide health coverage. According to the latest CBO projections for 2019, all these new revenues will amount to 0.49 percent of the nation's GDP.

Well, guess what: The Office of Tax Analysis, within the U.S. Department of the Treasury, has listed the top 10 tax hikes since 1940 (as a percentage of GDP) — and Obamacare will be tied for 10th. It'll share that ranking with the senior George Bush's 1990 tax hikes. Most notably, it'll rank far behind the 1982 tax hikes signed by Republican icon Ronald Reagan.

In an ideal world, the GOP would pay a political price for peddling its phony charge, but that's not how the game works. A huge share of the American public is still in the dark about the details of health reform, and is hence open to all manner of disinformation. The old Mark Twain line, about how a lie can circle the Earth before truth can lace its shoes, is apt in this circumstance.

The Obama White House clearly wants to dump the health-reform issue and move on — chief of staff Jack Lew says, "I don't think the American people want to have this debate again" — but that's classic Democratic naiveties, a passive attitude that has often proved fatal in the past. You can't defeat a falsehood unless you relentlessly confront it. If you let it metastasize, you lose.