His greatest achievement is also his biggest liability. It is the kind of paradox that would test the most agile of politicians, of whom Mitt Romney is not one.

So on Thursday, the former management consultant who is also a putative front-runner for the 2012 Republican presidential nomination turned to an old and reliable ally: the PowerPoint presentation. He was attempting to lay to rest criticism of the landmark health-care law he put into place as governor of Massachusetts, and to make a convincing case for how he would do things differently if he were elected president.

This will not be an easy pivot. The 2006 Massachusetts law made that state the first in the country to guarantee medical coverage to nearly every one of its citizens. It was also a model — as critics of Romney on both the left and right rarely miss an opportunity to point out — for the new federal law that has become Exhibit A in the conservatives’ case against President Obama.

“Our plan was a state solution to a state problem,” Romney said in his presentation to an audience of invited guests at the University of Michigan Cardiovascular Center. “[Obama’s] is a power grab by the federal government to put in place a one-size-fits-all system . . . a government takeover of health care.”

If he were president, Romney said, he would on his first day in office issue an executive order paving the wayfor states to opt out of the new federal law. In its place, he said, he would put forward a variety of measures that would give individual states more resources and flexibility to decide how to cover the uninsured, and to make the health-care market function more efficiently.

“It’s the same old plan the Republicans have been throwing out for years,” said Jonathan Gruber, a Massachusetts Institute of Technology economist who was a key health-care adviser to Romney when he was governor, and who later consulted with the Obama administration as it was putting together the new law. “It’s basically his effort to take health care off the table.”

There was a time, Romney noted, “when my Massachusetts health-care plan was considered, at least by me, to be an asset in my campaign.” Then he added: “I hear some laughter in the room.”

Elsewhere, the reaction has been much harsher than that. In a scathing editorial headlined “Obama’s Running Mate,” the editors of the Wall Street Journal’s conservative editorial page wrote Thursday that Romney’s record on health care amounts to “a fatal flaw.”

“The debate over ObamaCare and the larger entitlement state may be the central question of the 2012 election,” the editorial said. “On that question, Mr. Romney is compromised and not credible. If he does not change his message, he might as well try to knock off Joe Biden and get on the Obama ticket.”

Romney, who has announced a presidential exploratory committee, noted that many on the right have called upon him to renounce and apologize for the Massachusetts law. “There’s only one problem with that,” he said. “It wouldn’t be honest. I did what I thought was right for the people of my state.”

That hinted at another dimension of the challenge that he confronts on health care. The issue is not only an ideological test for Romney but also one that revisits the questions about his authenticity that have arisen as he has shifted or refocused his positions on other issues, including abortion and gun rights.

Shortly before the health-care presentation, the Democratic National Committee mockingly sent reporters a set of what it said were “missing slides,” comparing Romney’s past statements on the issue with his current ones.

GOP strategists inside and outside the Romney campaign say that it was inevitable that he would have to confront his rec­ord on the issue — and that it is better for him to do it sooner, rather than waiting until the presidential election kicks into full gear.

“This is what lawyers refer to as a bad fact. Not helpful, but probably not fatal,” said one GOP strategist, who is not affiliated with any of the 2012 contenders and spoke on the condition of anonymity to comment freely about a leader in the race. “Mitt has to pacify the base without repudiating the most central achievement of his governorship. It’s tricky, but possible.”

Presidential contests, especially in the early stages, are often a test of the candidates’ abilities to overcome their perceived flaws — and the 2012 GOP field, as it is shaping up, is amply endowed with those.

At a debate last week, former Minnesota governor Tim Paw­lenty apologized for his onetime support for a cap-and-trade system to deal with climate change. Newt Gingrich has directly confronted questions about his infidelities. And former Utah governor Jon Huntsman, who has just returned from a stint as Obama’s ambassador to China, has tried to ease worries about where his loyalties lie.

If Romney can satisfy concerns about his health-care plan, leading Republicans say, he will have eliminated one of the biggest obstacles on his path to the nomination.

“This is going to be far less of a disqualifier in a general election than it is in a Republican primary,” said Douglas Holtz-Eakin, who was chief economic adviser to Sen. John McCain’s 2008
presidential campaign, which sparred with Romney over the issue four years ago. “This election is, in the end, going to be a referendum on the president.”