His repeal refrain could become increasingly attractive to the opponents of the overhaul, and his campaign could make the case that a Romney victory is the next best chance to dismantle a law that's deeply unpopular with millions of people.
That's despite Romney's own support for the "individual mandate" in Massachusetts, where as governor he signed into law a state-based measure that ultimately helped serve as a model for the president's.
Romney struggled at times during the GOP primary campaign to reconcile his past support for the mandate and current pledge to repeal the federal measure. Obama's campaign has yet to capitalize with a general election audience on that apparent contradiction.
Romney may face big challenges even if the court strikes down all or part of the law. Attention would turn quickly to what he would do to help 50 million uninsured people get coverage and bring down the nation's spiraling health care costs.
He has promised to replace the measure with a handful of "common-sense" reforms, but has spent little time so far crafting a comprehensive plan.
"Whether all or part of Obamacare will have to be repealed, that's the first step, and that's the immediate priority," said Romney's domestic policy director, Oren Cass. "His goal will be to repeal anything that's left of Obamacare and actually sit down and identify the challenges we want to address and address them."
The Obama campaign would seize on Romney's opposition to the most popular provisions in the law. For example, Romney would not prevent health care companies from denying coverage to new customers with medical conditions. Nor would he force them to cover young adults on their parents' plans through age 26.
The candidates aren't the only ones working on their responses ahead of the court's ruling.
In a memo to fellow Republicans this past week, House Speaker John Boehner warned against "spiking of the ball" if the court strikes down the law.
GOP lawmakers say they quickly would mobilize repeal votes in the House if the court upholds at least some of the law. Similar congressional repeal attempts have been blocked by the Democratic-controlled Senate, and this renewed effort probably would end up the same way.
A congressional Republican aide said GOP lawmakers would try to replace the law, though those efforts would be slower and may not happen this year. The party's focus would be on controlling costs, not on ensuring coverage for all people, said the aide, who was not authorized to discuss the issue publicly and spoke on condition of anonymity.
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