Barack Obama’s signature domestic legislative achievement, the overhaul of the nation’s medical insurance system, was a huge political gamble from the start. It got through Congress by the narrowest of margins in the spring of 2010, and seven months later, it clearly played a major role in the Democrats’ loss of their control of the House. Today, polls reveal a public that remains deeply divided about the law, with more than half of those surveyed by the nonpartisan Kaiser Family Foundation reporting an unfavorable view.

The risk the president took in putting so much of his political capital behind the legislation will be no more evident than when the next election returns come in from Florida, a state that may well determine whether Obama stays for a second term. While the initially intense political attention to the law’s consequences has faded in much of the country — overtaken, mainly, by the balky economy and high unemployment — the voters of Florida have been inundated with a steady flow of news about the fate of the statute because it’s the state’s attorney general who has pursued the most visible challenge to the law’s constitutionality.

The Supreme Court is expected to rule in the Florida case by the end of June, four months before Election Day. Whether the court upholds the law, throws it out altogether, strikes down only some parts or punts the whole question back to the lower courts, the decision is sure to revive and intensify the debate about the merits of the law, which polls show to be slightly more unpopular in Florida than nationally.

Obama carried the state in 2008 by a narrow but unambiguous 2.5 points, and his coattails helped the Democrats pick up a pair of House seats, for a total of 10 in a delegation of 25. But the Republican midterm tide more than reversed those gains, and at the moment, there are 19 Republicans and just six Democrats from Florida in the House. Conservatives undeniably dominate the state’s power structure at the moment; Republicans hold 2-to-1 majorities in both halves of the Legislature and all but one statewide office. (The exception is Sen. Bill Nelson, and he faces a potentially difficult third-term election campaign next year.)

Although health care issues are not as high on Florida voters’ agendas as job creation and, in some areas, the deflated housing market, public policy experts in the state say the health care overhaul is sure to have an effect on Democrats’ chances a year from now.

“Floridians take a great deal of proprietary interest in the health care case,” said Carol Weissert, a political science professor at Florida State University. “It will probably be among the top two or three campaign issues. Health care will be spun in a way to help the Republican cause, and I do think that attacks will be effective.”

The health care law “will probably cost him a few points in Florida,” Terri Fine, a political science professor at the University of Central Florida, predicted of the president. A few points wouldn’t matter in some states. In Florida, recent history shows that a handful of votes can change history.

A State to Win

Since 1960, no one has been elected president without carrying at least two of the three biggest perennial battleground states: Florida, Ohio and Pennsylvania. And Florida’s importance will only be magnified next year because it was awarded two more House seats in reapportionment and now has 29 electoral votes — more than 10 percent of the total needed to win the White House. Ohio, meanwhile, has lost a pair of electoral votes (to a new total of 18) and Pennsylvania has lost one (to 20).

Presidential margins in Florida have varied between relatively close and infinitesimal every year since 1992, when President George H.W. Bush carried the state by 2 points (100,130 votes). Eight years later, the entire nation waited through 35 days of legal and political maneuvering until the Supreme Court effectively awarded the state’s electoral votes, and therefore the presidency, to George W. Bush. His official margin of victory: 537 votes out of nearly 6 million cast.

Recent polls suggest that the presidential race will be close in Florida once again. Two recent polls in the state showed the Republican frontrunner, Mitt Romney, besting Obama, but only by statistically insignificant margins.

One of those surveys, by Quinnipiac University, pegged the president’s approval rating in the state at just 41 percent with only 43 percent saying he deserves to be re-elected.

The health care issue is not the main reason Floridians are dissatisfied with the president’s performance, but it is a factor. When asked by Quinnipiac to single out one issue that is most important to them, about 55 percent said the economy. Health care was the third-highest issue cited by Florida respondents, closely following concerns about the federal deficit.

On Both Sides of the Law

The rhetoric over health care is likely to heat up as the Supreme Court hears arguments in the Florida case in March. The justices will consider whether some provisions in the law — those that require most individuals to purchase medical insurance and expand Medicaid, the federal-state program for the poor — are constitutional.

To be sure, it may be more difficult for Republicans to hammer Obama on the health care law if Romney is the Republican nominee. As governor of Massachusetts, he signed a health care measure in 2006 that includes many elements similar to the federal law, including an individual mandate. Obama has said the Massachusetts law served as a model for the federal legislation. Romney, of course, prefers to highlight the numerous differences between the two statutes — and points out that what is good for one state is not necessarily best for the entire country. But those nuances can tend to get lost in the clamor of a campaign.

Even if Romney is at the top of the ticket, though, Florida Republican candidates at all levels are likely to include criticisms of the health care law in their talking points. The frontrunner for the party’s Senate nomination, Rep. Connie Mack IV, has been a particularly vocal critic in the House. And Republicans in the state Legislature also are expected to keep up their criticisms. Earlier this year, the state House and state Senate endorsed amending the Florida constitution to bar a health insurance mandate; the language has a good shot at being ratified by the voters next fall, when it will be on the same ballot as the presidential race.

The reaction of Floridians to arguments for or against the federal law varies in part because Florida is a diverse state with a number of distinct constituencies. It has a significant retiree population, some of whom aren’t yet 65 and so don’t qualify for Medicare, the federal health insurance for the elderly. These younger retirees — particularly those who would have a hard time buying insurance because of preexisting conditions — would potentially benefit in 2014 from the new insurance coverage options that would become available under the health care law. But many voters now on Medicare, or who soon will be, are nervous that the law’s Independent Payment Advisory Board will result in the rationing of care.

Recent college graduates might be happy they can take advantage of a provision that allows them to stay on their parents’ insurance until age 26. But health policy professors such as Fine and University of South Florida’s Susan MacManus say most college students and recent graduates are relatively healthy and so view insurance as a far less pressing issue than securing a paycheck.

The state’s large immigrant population could benefit from the subsidized coverage coming in 2014, either through private insurance overseen by the government or through Medicaid. Those options are available only to people who are in the country legally, although the enforcement mechanism for that provision has been called into question. (About one-third of the people in the country who will still lack coverage after the health care law takes hold will be illegal immigrants, according to the Congressional Budget Office.)

To counter such concerns, liberal interest groups have established a program, dubbed “Know Your Care,” that will hold a series of town hall meetings across Florida to promote the law. The meetings will be geared toward seniors, Hispanics and college students. Meetings have been planned for Orlando, Broward County and Tallahassee.

And the Obama administration is intensifying its efforts to visit Florida. Health and Human Services Secretary Kathleen Sebelius has been in the state regularly this year, sometimes accompanied by Attorney General Eric Holder as the pair talks about new efforts to crack down on Medicare fraud. This fall, first lady Michelle Obama and Vice President Joseph Biden made treks to the state.

And when speaking to one Florida audience, the vice president seemed to acknowledge the difficult reality he and Obama face there next year. Adopting an aphorism made famous by former Boston Mayor Kevin White, Biden requested: “Don’t compare me to the Almighty; just compare me to the alternative.”