Mitt Romney’s presidential campaign on Monday rejected a Republican attack on the Affordable Care Act, repudiating a contention made in last week’s Supreme Court decision that the law’s requirement that individuals carry medical coverage amounts to a tax.

The Romney team’s refusal to invoke the word “tax” with regard to the individual mandate puts the candidate at odds with others in his party at a moment when Republicans are attempting to capi­tal­ize on the Supreme Court’s decision, which deemed President Obama’s health-care law constitutional. Some Republican-led states are trying to thwart the legislation’s effort to cover the poor.

In an interview Monday on MSNBC, Romney campaign senior adviser Eric Fehrnstrom said the former Massachusetts governor “disagrees with the court’s ruling that the mandate was a tax.”

Although disappointing to conservatives, the justices’ decision contained what they regard as two silver linings: the potential to fuel political opposition to the law and a path to undermine its substance.

First, in ruling that Congress has the ability under its taxation power to fine people who choose not to have health coverage, the court undercut Obama’s credibility on how to define that provision. The president had insisted repeatedly that it is not a tax.

Republicans and their allies seized on that part of the decision and are running ads that highlight it.

“The president said it was not a tax,” Senate Minority Leader Mitch McConnell (Ky.) said in an interview on “Fox News Sunday.” “The Supreme Court, which has the final say, says it is a tax.”

Second, the court overturned a part of the law that would allow the federal government to take away Medicaid funding from states that do not expand their programs to cover everyone earning up to 133 percent of the federal poverty level.

The new law offers federal funding to foot nearly the entire bill for adding those newly eligible to the Medicaid rolls. But in a move that threatens to undercut the law’s goal of covering those who lack health insurance, the Republican governors of at least four states — Florida, Iowa, Louisiana and South Carolina — have said that they probably will turn down that additional money from Washington rather than broaden their Medicaid eligibility.

Romney’s resistance to calling the individual mandate a tax reflects an awkward history that has dogged his presidential campaign: Although he decries the federal health-care law and vows to lead an effort to repeal it if he is elected, Romney championed and signed very similar legislation when he was governor of Massachusetts.

As the federal law does, the 2006 Massachusetts law imposed a fine on people who refused to buy health coverage. And as Obama does, Romney insisted that it was not a tax. He referred to it as a “penalty” and an “incentive.”

That Fehrnstrom continued to hew to that language with regard to the federal law had the campaign scrambling to explain a position that is at odds with a new favorite talking point of many GOP leaders.

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

But one conservative activist said he is not bothered by the dissonance.

“Because the court did this bizarre runaround, the criticism of the court gets convoluted, too,” said Grover Norquist, president of Americans for Tax Reform, whose anti-tax pledge has become part of Republican dogma.

“It’s clear enough which team everybody is on,” he added.

How well the law works will hinge in large part on how willing and adept states are at implementing it. They have two major roles: building the “exchanges” that will act as insurance marketplaces and expanding coverage for low-income people through Medicaid.

The most significant indication of how much resistance it is likely to face in Republican-led states has come from Florida.

“Floridians are interested in jobs and economic growth, a quality education for their children, and keeping the cost of living low,” Gov. Rick Scott said in a statement Sunday night. “Neither of these provisions in ObamaCare will achieve those goals, and since Florida is legally allowed to opt out, that’s the right decision for our citizens.”

If Florida chooses not to build an exchange, the law provides for the federal government to do it for the state. But it would be a trickier issue if the state refuses to expand its Medicaid program.

After California and Texas, the most uninsured people who would have gained coverage through Medicaid expansion reside in Florida. The combined effect of Florida, Iowa, Louisiana and South Carolina opting out would be to reduce the number of people who gain Medicaid through the law by 11 percent.

Scott contended that even though the federal government will initially cover the full cost, “the burden increasingly shifts to Florida taxpayers in future years . . . and education funding will be adversely impacted if we do not control the growth in Medicaid spending.”

Advocates for the poor noted that close to 1 million Florida residents — about one-fourth of the state’s uninsured — would have gained coverage through the expansion.

“We think it’s just grossly irresponsible,” said Leah Barber-Heinz, a spokeswoman for Florida CHAIN, a consumer advocacy group. “And we also know that over the next decade, Florida would have received billions in Medicaid funding that we would be turning away, and will then go to other states. It’s tragic for the state of Florida.”

Lane Wright, a spokesman for Scott, countered that although Florida does not offer Medicaid to childless adults, it provides Medicaid to parents with incomes up to 133 percent of the poverty level. “Those who are most in need in Florida are already getting taken care of,” he said.