Obama began by pointing to the law Romney enacted while governor of Massachusetts, which included a similar fine assessed to people who choose not to obtain health insurance.
"On the health care bill, Mr. Romney was one of the biggest promoters of the individual mandate," the president said in the interview with WLWT in Cincinnati. "In Massachusetts, his whole idea was that we shouldn't have people who can afford to get health insurance to not buy it and then force you or me, or John Q. Public to have to pay for him when he gets sick."
The so-called "individual mandate" was deemed constitutional last week by the U.S. Supreme Court. The 5-4 decision upheld the mandate under Congress' powers of taxation.
Most Republicans, eager to portray Obama as raising taxes on the middle class, immediately labeled the mandate a tax while vowing to repeal the law in Congress. But Romney's campaign, in a politically vulnerable spot given the similar mandate he enacted as governor of Massachusetts, labeled the fine a "penalty" on Monday.
The next day, the chairman of the Republican National Committee made an attempt at party unity, saying on CNN: "Our position is the same as Mitt Romney's position. It's a tax."
Romney himself weighed in on Wednesday, saying that while he agreed with the court's dissent that the mandate was unconstitutional, he accepted the majority ruling that the fine assessed to people who choose not to obtain health insurance amounted to a "tax."
He maintained, however, that the similar Massachusetts fine was a "penalty" since states have a power to assess mandates and the federal government does not.
In the interview Friday, Obama said the reversal from "penalty" to "tax" could be explained purely by politics.
"The question becomes, are you doing that because of politics?" Obama asked. "Are you abandoning a principle that you fought for, for six years simply because you're getting pressure for two days from Rush Limbaugh or some critics in Washington?"
Obama, using his position as an incumbent, said the presidency required more consistency than Romney was displaying.
"One of the things that you learn as President is that what you say matters and your principles matter. And sometimes, you've got to fight for things that you believe in and you can't just switch on a dime," Obama said.
Romney's campaign, in a statement, flipped that assertion back on the president.
"President Obama is right – as president, what you say matters," Romney spokesman Amanda Henneberg wrote in a statement. "It matters that President Obama told the American people that Obamacare was not a new tax, then sent his lawyers to convince the Supreme Court that it was a new tax, and now is insisting – again – that it is not a tax. Americans deserve straight answers from their president. Mitt Romney believes Obamacare is a job-killing law that raises a whole series of taxes, cuts Medicare, and gets between patients and their doctors. In order to repeal Obamacare, we must replace President Obama."
Despite Obama's assertion that Romney switched from "tax" to "penalty" for political purposes, his own campaign hasn't been immune from spinning the decision to downplay the justice's ruling that the mandate can only stand as a tax.
Asked Thursday whether Obama "disagrees with the Supreme Court decision that says it's now a tax," campaign press secretary Ben LaBolt said "that's right."
"He's said it was a penalty," LaBolt continued. "You saw our arguments before the court."
And Jay Carney, White House press secretary, said again Thursday "this is clearly a penalty."
Obama's solicitor general, however, did argue in March that the individual mandate could be viewed as constitutional under Congress' taxation power. Donald Verrilli said the fee would be collected by the Internal Revenue Service on April 15, the day Americans pay their federal income taxes.