He puts on a charming smile and projects and air of confidence in public, but underneath it all there's a disconcerting fact chipping away at Mitt Romney. Opposition to the sweeping healthcare reform law has become a centerpiece of the Republican strategy and will undoubtedly be a key issue in several election cycles to come. So Romney, the Republican favourite for president in 2012, has positioned himself as a leading critic of President Obama's plan.

But there's a small problem: in 2006, as governor of Massachusetts, Romney introduced and signed into a law a slate of health reforms virtually identical to the plan Obama has now enacted on a nationwide level. Don't take my word for it. The conservative Wall Street Journal editorial board weeks ago labelled the Romney and Obama laws "fraternal policy twins", noting that the former governor "signed a prototype of ObamaCare into law in Massachusetts." The rightwing Cato Institute said the two plans "almost perfectly mirror" each other.

Whether it's the individual mandate, the subsidies, the taxes, the insurance regulations or the exchanges – the bills use all the same means to achieve all the same goals. Romney has tied himself in knots trying to obscure this awkward fact, even as the media recognises that by criticising the Obama plan he's essentially bashing his own greatest legislative accomplishment.

The Associated Press recently ran a story headlined Romney attacks health care law similar to his own. The Christian Science Monitor wondered, Who is the father of health care reform: Obama or Mitt Romney? Columnist Gail Collins of the New York Times jestingly called Romney a "liberal icon". Even Fox News, largely a communications arm of the GOP, grilled him on his duplicity.

"A lot of commentators have said this is sort of similar to the bill that Mitt Romney, the Republican governor and now presidential candidate, passed in Massachusetts," Obama said during a recent appearance on NBC News, grinning from ear to ear.

When you cut through the fluff, the only case Romney can still make is that "socialism" and a "big-government takeover of healthcare" is acceptable on a state level but not on a federal level. He's stretched that argument as far as possible, alleging yesterday in an interview that Obama's bill is an unconstitutional violation of the 10th amendment, which protects states' rights.

What's even more uncomfortable for the Republican political orbit is that the core ideas in both bills were cultivated by the staunchly conservative Heritage Foundation thinktank (which now claims Obama has downgraded America from "free" to "mostly free") last decade.

So, the substantive basis of the new law was crafted by the rightwing establishment, and its architecture embraced by a top Republican a few years ago. (It's also very similar to the Republican alternative to the failed Clinton-care effort in the 1990s.) Yet it's been viciously assaulted by Republicans and conservatives as a tyrannical government takeover. What gives?

The most logical explanation is that the GOP decided from minute one of the Obama presidency that its plan of attack would be to prey on constituents' fears and paint him and his Democratic allies as nefarious socialist sympathisers, regardless of what they actually do.

Armed with a powerful message machine and devoid of any desire to fix the healthcare system, Republicans deemed this their best chance to undercut the new president and win back power. Jim DeMint made this clear by saying he wanted health reform to be Obama's Waterloo.

And from top to bottom, the conservative movement snapped in line, obediently promulgating the party's talking points and stifling dissent from within. Anybody who strayed from the narrative was a RINO, a moonbat, a closeted liberal. Even tactical criticisms from insiders who opposed the bill were off limits, as former Bush adviser David Frum learned.

Above all, this saga reflects the rightward gravitational pull in the US political spectrum. It's been happening for decades. Republicans grow increasingly conservative to differentiate themselves and appease their corporate constituency; Democrats, in response, tack rightward in fear of losing their big-money donors and being castigated as socialists.

Healthcare is the perfect example of this phenomenon unfolding. The Democratic health reform proposals during the last century have become increasingly conservative over time, but the GOP lines of attack haven't changed. No matter what the substance, they're derided as Marxist prototypes that will seriously threaten the future of freedom in America.

Unfortunately for Republicans and their leading presidential contender, this is one instance where they probably won't be able to win back power by redefining the centre.