Mitt Romney's campaign veered off the Republican Party's message Monday, saying the Supreme Court was mistaken when it ruled last week that the individual mandate that funds President Obama's health care law is a tax.

Republicans had been quick to seize on what they saw as a promising new line of attack on the Obama health care overhaul after Chief Justice John Roberts sided with the court's liberal justices to uphold the health care law while declaring its central financing provision -- a requirement that virtually everyone buy health insurance or pay a penalty -- was effectively a tax.

At first, Romney appeared to be on board with the party message that the Patient Protection and Affordable Care Act amounted to a multibillion-dollar tax on the American public that would only further undermine an economic recovery. "Obamacare raises taxes on the American people by approximately $500 billion," Romney said last week.

But Romney's message changed Monday, apparently out of concern that any attempt to portray Obama's mandate as a tax would open Romney to criticisms that he, too, has raised taxes. Romney implemented health care reforms very similar to Obama's, including requiring all state residents to buy insurance, when he was governor of Massachusetts. Like Obama, Romney has always insisted that the requirement did not amount to a tax.

"The governor has consistently described the mandate in Massachusetts as a penalty," Romney senior strategist Eric Fehrnstrom said on MSNBC. "He agreed with the dissent that was written by Justice [Antonin] Scalia, which very clearly stated that the [Obama] mandate was not a tax."

Romney's awkward strategy shift highlighted a concern first raised about him by Pennsylvania Sen. Rick Santorum during the Republican primary. Santorum claimed that Romney is "the worst Republican in the country to put against Obama on the issue of health care" because Romney had instituted similar reforms himself, undermining his own claims that he would repeal Obama's health care law if elected president.

Democrats insist the penalty that would be paid by people without insurance is not a tax. Still, Republicans have gleefully assailed the president not only for raising taxes but for misleading the public about the possibility of a tax increase.

"Even though the president tried to admit for over a year that it wasn't a tax, nobody believed it, and now we know it," House Speaker John Boehner, R-Ohio, said on CBS' "Face the Nation."

According to some analysts, the health care fallout is indicative of a potentially larger albatross for Romney -- his inability to present a cohesive message as campaign issues shift.

Already, they note, Obama has put Romney on the defensive on immigration by announcing his administration would no longer deport young people in the country illegally. Romney pledged to overturn the directive but didn't say what he would do with the millions of illegal immigrants already in the country. Obama also appeared to catch Romney off guard on the issues of same-sex marriage and contraceptives.

"Here we go again," lamented one GOP strategist. "I swear, this one really makes me wonder what they're thinking in Boston. Just call it a tax increase; it's an easy argument."