An adviser to former Massachusetts governor Mitt Romney broke from the messaging of other Republicans Monday, arguing that the health-care mandate in the Affordable Care Act is not a tax.

“The governor disagreed with the ruling of the court, he agreed with the dissent that was written by Justice Scalia, that very clearly said that the mandate was not a tax,” Eric Fehrnstrom said on MSNBC. “The governor believes what we put in place in Massachusetts was a penalty and he disagrees with the Court’s ruling that the mandate was a tax.”

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Since the Supreme Court ruled that the mandate was constitutional as a tax rather than under the Commerce Clause, Republicans have attacked Democrats from that angle.

Romney is in an awkward position, because his individual mandate in Massachusetts also imposed a penalty on those who did not buy insurance. If such penalties are taxes, than he raised taxes as governor.

That means that on this one issue, Romney agrees with Democrats, who are resisting labelling the mandate a tax despite the ruling.

“The Supreme Court has spoken. This law is a tax,” said Senate Minority Leader Mitch McConnell (R-Ky.).

“Now it’s official,” a recent anti-Democratic ad from the outside group American Crossroads said. “Obama increased taxes on struggling families.”

But Romney himself has steered clear of this argument. In his statement after the ruling, he did not comment on the individual mandate penalty as a tax.

In a statement Monday, the Republican’s campaign dared Obama to embrace the law as a tax while again avoiding that label.

“The Supreme Court left President Obama with two choices: the federal individual mandate in Obamacare is either a constitutional tax or an unconstitutional penalty,” said Romney campaign spokeswoman Amanda Henneberg. “Governor Romney thinks it is an unconstitutional penalty. What is President Obama’s position: Is his federal mandate unconstitutional or is it a tax?”

Congressional Republican aides tell the Plum Line that the two messages are not in conflict. Republicans, one aide argued, agree with the dissent — that the mandate is not a tax but an unconstitutional overreach — but now that it is defined as a tax, it can be criticized as such.

But that line of attack is more easily maintained by Republicans who never imposed any such mandate.