Washington (CNN) -- Rick Santorum went to the steps of the U.S. Supreme Court on Monday to attack front-running Republican presidential rival Mitt Romney over the federal health care reform law being argued inside this week.
Framing the legal challenge to the 2010 health care law as a question of "basic liberty in our society," Santorum said Romney lacks credibility in opposing health care reform because he implemented a similar system in Massachusetts when he was governor.
"There is one candidate in this race who can actually make the contrast that is necessary between the Republican position -- the conservative position ... and one that (President) Barack Obama believes in -- and that's Rick Santorum," the former Pennsylvania senator told reporters.
Santorum called Romney "uniquely disqualified to make the case" against the Patient Protection and Affordable Care Act, which critics refer to as "Obamacare" because it was championed by the president.
"He's the worst candidate to go against Barack Obama on the most important issue of the day," Santorum said.
The comments illustrated ramped-up rhetoric during an off week in the Republican campaign before the next primaries in Wisconsin, Maryland and the District of Columbia on April 3.
Coming off Saturday's strong victory in Louisiana, the conservative Santorum is trying to maintain momentum as the race heads for states considered friendlier territory for the more moderate Romney, who has a 2-to-1 lead in delegates.
According to CNN's unofficial estimates, Romney has 569 delegates compared with 262 for Santorum, 136 for former House Speaker Newt Gingrich and 71 for Texas Rep. Ron Paul. It takes 1,144 to secure the Republican nomination.
Romney campaigned Monday in California, telling an event in San Diego that the health care reform law was "an attack on free enterprise, an attack on economic freedom unlike anything we have ever seen before."
Speaking at NuVasive, a medical device company that designs artificial spine replacements, Romney said a new tax on medical device companies under the health care law could force the business to eliminate 200 jobs.
"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.
A CNN/ORC International Poll released Monday showed that the health care law is increasing in popularity, especially among independent voters, but half of all Americans still oppose it.
According to the poll, 43% of Americans approve of the law, up 5 points from November, with 50% saying they disapprove, a drop of 6 points. Of those who oppose the measure, 37% said it was too liberal and 10% said it wasn't liberal enough.
The health care issue prompted an emotional debate when the law moved through Congress in 2009 and 2010, and it continues to create controversy.
On Sunday, Santorum used a profanity in responding to a New York Times reporter asking about Santorum's assessment of Romney as the "worst Republican in the country" to run in November. Santorum insisted he was talking in the context of the health care issue and called the reporter's question an attempt to distort his words, saying "It's bulls---."
Santorum refused to back down Monday over the exchange, saying: "If you're a conservative and you haven't taken on a New York Times reporter, you're not worth your salt, as far as I'm concerned."
In an interview on CNN's "The Situation Room," Santorum said the confrontation was ginned up by Romney campaign operatives.
"They sent a Romney person to our speech," he said. "He fed the line to all the reporters, and we saw it happening. And every man in that room, even the reporters, said, 'Oh, yeah, we understood what you meant. But the Romney people said this to us, so we had to ask about it.' That's what happened."
But a top Romney surrogate said Santorum's heated exchange with the reporter showed he lacked the temperament to serve as president.
"Sen. Santorum has lost his personal discipline and self control in the process," former New Hampshire Gov. John Sununu said on a conference call with reporters. "It's one thing to lose your temper at a New York Times reporter and it's another to have to deal with the pressures of folks on the international stage and even opposing congressional leaders."
Sununu also suggested Santorum should drop out of the race so Republicans can unite in support of Romney. The proposal drew a scornful response from Santorum.
"After I won Louisiana by 23 points?" Santorum said. "I understand the game, but this is, you talk about desperate and pathetic, Mitt Romney can't run on his record."
Santorum has made his opposition to the health care reform law a central campaign theme, repeatedly attacking Romney for the Massachusetts law that preceded the federal version.
"This was a disaster in Massachusetts and then he had the audacity to go out in 2009 and argue that Barack Obama follow his lead," Santorum said outside the Supreme Court. "Unfortunately for the country, Obama did. President Obama did follow Mitt Romney's lead."
Romney contends his program was only designed for Massachusetts and that he would seek to repeal the federal plan if elected president.
However, the health care issue continues to haunt Romney on the campaign trail.
Obama's senior adviser, David Plouffe, made sure to highlight the Romney-Obama link on health care during appearances on Sunday talk shows.
"Mitt Romney is the godfather of our health care plan," Plouffe said on the NBC program "Meet the Press," noting that now Romney was "running away from that."
To Santorum, it all comes down to growing concern on the political right about whether Romney truly holds conservative beliefs he has declared during the GOP campaign or will revert to more moderate stances of the past once the nomination is secured.
However, pressure is mounting from mainstream Republicans for Santorum and Gingrich to drop out of the race so the party can coalesce around what many consider to be Romney's inevitable nomination.
Gingrich, who has won only two states -- South Carolina and his home state of Georgia -- has vowed to stay in the race until the Republican convention in Florida.
Conservative Sen. Lindsey Graham of South Carolina made it clear Sunday that he expects Romney to be his party's nominee, even though he has yet to make a formal endorsement.
"I think the primary's over. Romney will be the nominee," Graham said on CNN's "State of the Union." "I'm very comfortable with him ... he'll get to 1,144."
Santorum and Gingrich have run "phenomenal races," Graham said, but now was the time for Republicans of all stripes to work together to defeat Obama in November.
CNN's Gabriella Schwarz, Shawna Shepherd and Shannon Travis contributed to this report.