Obama has pledged to carry it out, but fiscal concerns and political pressure could drive him to alter provisions. Meanwhile, Romney's vow to repeal the law is unlikely to be realized, but he could still have a strong impact on it.
On the presidential campaign trail, Republican Mitt Romney has repeatedly called for repeal of the 2010 health law. President Barack Obama has vowed to implement it. Both men could face obstacles: Romney may be stymied by the lack of a majority in Congress to do his will, and Obama could be forced by fiscal concerns or public opinion to revamp parts of the law.
Here is a look at how Obama and Romney might change the health law in the years ahead based on interviews with health policy experts.
President Barack Obama has urged voters to re-elect him so that he can put the law fully into effect. But some analysts predict the mounting pressures to reduce federal spending will complicate that plan. And others note that in a second term, Obama may be more open to working with Congress to tweak provisions of the law that have raised concerns. Leading up to this tight election, Obama and Democrats have been reluctant to make modifications to the law, known as the Affordable Care Act (ACA).
"Right now (Democrats) can't criticize the ACA. It's just not politically smart," said Dan Mendelson, chief executive of the consulting firm Avalere Health who oversaw health programs at the Clinton administration's Office of Management and Budget. But should Obama win a second term and Democrats retain control of the Senate, "I think that adjustments are on the table" as part of a larger deal to reduce the federal deficit, he said.
Scale Back Subsidies: As part of that effort to reduce federal spending, there could be pressure to scale back the health law's subsidies that help low-income residents afford coverage. People who earn up to 400 percent of poverty - currently about $92,000 for a family of four - are eligible to get financial help in purchasing coverage. Another big-ticket item is the expansion of Medicaid coverage to anyone up to 133 percent of the poverty level, or about $30,656 for a family of four.
The ACA is "so vast that by default it has to be impacted if there is a bipartisan, grand bargain debt deal," said Mike Tuffin, managing director of the consulting firm APCO Worldwide's Washington, D.C., office and formerly executive vice president of America's Health Insurance Plans, an insurance industry trade group. "You can imagine the subsidies being impacted, the Medicaid expansion being impacted."
Changing the law's implementation schedule is wishful thinking among Republicans, Mendelson said. Any delay in full implementation could risk political backlash from consumers, who have waited years for the major provisions of the ACA to kick in. Delays may also open the law to other changes that Obama and Democrats don't want.
"My feeling is that it would be a major political liability for the president to encourage delay," he said, "and that if this is going to be his legacy, I see no indication from the policy makers that they either want or expect there to be a delay."
The president "is willing to work with anyone with good ideas to improve the Affordable Care Act. What he is not willing to do is reopen old partisan battles over the central guarantees of Obamacare," said Adam Fetcher, a spokesman for the Obama campaign.
Change in Age Rating Bands: The ACA prohibits insurers from charging more than three times as much for a policy sold to an older person than to a younger person. (This does not affect people over 65 who are covered by Medicare.) This is a change from current law in most states where there are no limits on how much more insurers can charge older people. America's Health Insurance Plans is advocating that the law's rating bands be changed to 5:1 to prevent what the group describes as "rate shock" for younger people and families.
The issue that arises is that the law "makes coverage more affordable for the elderly but more expensive for the young people they want to buy coverage," said Paul Heldman, senior health policy analyst with Potomac Research Group, a Washington research firm.
Medical Device Tax Cut: Of the many taxes in the health law, one has come under especially withering criticism: a 2.3 percent tax on the sale of any taxable medical device. Medical device manufacturers have loudly opposed the tax and won some key congressional support.
"For some, it could truly be the difference between surviving and having to close their doors," Michael R. Minogue, CEO and chairman of the board of Abiomed, Inc., which makes cardiac medical devices, told Congress this summer. But other analysts contend that the industry will do better under the law because more people will have coverage for treatments that use medical devices.
Legislation to repeal the tax passed the House in June with 37 Democrats joining Republicans to support the measure, although it is unlikely to receive Senate consideration this year.
The problem with this - or any change - in the law's taxes is finding another area to make up the loss of revenue. "It's easy to hate a tax. It's harder to find a pay for," says Mendelson.
Nonetheless, Tuffin says that this and other taxes could raise concerns if the public sees them as making health insurance or medical care more expensive.
"All of those hit simultaneously and overnight in 2014 and they are going to drive up the cost of coverage," he says. "Consumers are going to feel that, small businesses are going to feel that."
IPAB: One of the most contentious provisions of the health law is the creation of a 15-member panel charged with making recommendations to reduce Medicare spending. if the amount the government spends grows beyond a target rate. Congress must pass alternative cuts of the same size, or the recommendations from the panel, known as the Independent Payment Advisory Board (IPAB), become law. IPAB members are prohibited from making recommendations that would increase revenues or change benefits, eligibility, or Medicare beneficiary cost-sharing.