Health care was supposed to be Mitt Romney’s Achilles’ heel: The state overhaul he championed as governor of Massachusetts is so similar to the sweeping federal law conservatives deride as “Obamacare” that it was once widely regarded as a big enough liability to doom his presidential chances.

But Romney remains the overwhelming favorite in a topsy-turvy campaign in which health care has rarely been the driving issue, and he is picking up the support of prominent conservatives as he moves toward securing his party’s nomination.

This week, as the Supreme Court reviews the Obama administration’s health-care law, Romney’s remaining opponents for the Republican presidential nomination are trying to capi­tal­ize on what may be one of their last opportunities to deny him the prize.

Rick Santorum is urgently attacking “Romneycare,” arguing that Romney would effectively forfeit one of the biggest issues Republicans have to run against Obama.

Santorum pounces

His campaign has fired off daily e-mails and videos highlighting the Massachusetts law, while the former senator from Pennsylvania has been particularly animated in talking about the issue; he uttered an expletive Sunday night at a New York Times reporter who asked him to clarify his line of attack on Romney.

“It’s the best opportunity for us to make the case about big government, to make the case about individual liberty, to make the case about budget deficits being blown wide open, to make the case about people not getting quality health care and have rationing of health care and government mandating you and making you do something against your economic interests, against your religious interests,” Santorum told reporters Monday over breakfast in Washington.

Calling health care “the mega issue,” he argued that Romney is “the one guy who can’t make the case.”

To emphasize his differences with Romney on health care, Santorum held a campaign event Monday on the steps of the ­Supreme Court as the justices were concluding the first of three days of oral arguments.

He told reporters that the Massachusetts law is “one of the reasons the jury’s still very much out” on Romney’s candidacy.

GOP voters cite economy

But it is difficult to measure how much it has hurt Romney in the nominating contest. Just 6 percent of Republicans nationally rated health care as the top issue, well behind the economy and general dissatisfaction with government, in a March Gallup poll. In January, a Washington Post-ABC News poll found that 27 percent of Republicans and GOP-leaning independents said Romney’s health-care record was a major reason to oppose him. But 21 percent saw it as a reason to support him.

Romney’s biggest problem may be that his overhaul in Massachusetts places him ideologically to the left of much of the GOP base. In three big states whose primaries Romney won — Florida, Illinois and Ohio — about four in 10 Republican voters called Romney “not conservative enough” in exit polls.

“It’s clearly a vulnerability for Governor Romney, but by coming out so strongly for repealing and replacing Obamacare, while he may not have completely neutralized the issue, he’s taken a good deal of the sting out of it,” GOP pollster Whit Ayres said.

Romney has been trying to neutralize his problems with the conservative opponents of the Obama law by recommitting to repealing it.

“There are a lot of reasons not to like Obamacare,” he said Monday during a campaign stop in San Diego. “My colleagues the other day listed a whole series of them — and there are about 30 things — and I chuckled as I looked down, just shaking my head at the things Obamacare is doing.”

But Romney is picking up more conservative support as impediments to his nomination appear to be diminishing. On Monday, he trumpeted the endorsements of a handful of prominent conservative leaders — House Majority Whip Kevin McCarthy (Calif.), American Conservative Union Chairman Al Cardenas and tea party star Sen. Mike Lee (Utah) — who called on Republicans to unite behind Romney.

Repackaging issue

Looking toward a campaign against the president this fall, Romney has begun to frame the health-care law as just one part of a broader overreach by the administration, which he says represents “an attack on economic freedom unlike anything we have ever seen before.”

Yet as Romney visited a medical-device company here that makes artificial spines, delivering a speech in front of a banner that read “Repeal and Replace Obamacare,” he did not directly call for its repeal. Nor did he refer to the week’s activity at the Supreme Court.

And although Romney stands by the Massachusetts program and has at times detailed the differences between it and the federal overhaul, he made no mention of it on Monday.

Instead, he spoke broadly about what he considers a culture of government regulation and taxation brought on by the Obama administration.

“I just don’t think the president and his people understand that as they burden enterprise with taxation and with regulation, they hurt all of us,” Romney said. “This is not just about the business itself being attacked, bad enough as that is, and the employees who work there being attacked, bad enough as that is, but the entire economy, all of America, slows down.”

Romney repeatedly referred to NuVasive, the company that hosted him Monday, and noted that its chief executive, Alexis V. Lukianov, emigrated from Russia to start the business.

“These dreams that people like Alex have had, these dreams are crushed — tax by tax, regulator by regulator, regulation by regulation,” Romney said. “Washington is crushing the dreams and crushing the dreamers. We can’t let it happen.”

Balz reported from Washington. Polling analyst Scott Clement in Washington contributed to this report.