The Supreme Court’s skeptical consideration of President Obama’s landmark health-care legislation this week has forced his supporters to contemplate the unthinkable: that the justices could throw out the law and destroy the most far-reaching accomplishment of the Obama presidency.

The fate of the Patient Protection and Affordable Care Act is uncertain. A ruling is not expected until June. White House officials are refusing publicly to consider that the law might be struck down or to discuss contingency plans, insisting that they do not address hypothetical questions.

Other Democrats have begun assessing how such an outcome could affect the political landscape of 2012, with some surmising that a backlash against Republicans could follow a ruling against the law. But supporters argue that on a substantive level, the results would be devastating.

“This would be a great loss, obviously, to the American people,” said Rep. Chris Van Hollen (D-Md.) “The status quo with respect to the health insurance system was unacceptable to the American people. This was an answer to a very real problem.”

By the time oral arguments ended this week, supporters were rattled by the tough questions, with legal scholars and others observing that a majority of the justices seemed inclined to strike down the law’s key provision, an individual mandate to obtain health insurance.

That has prompted a larger conversation about what happens if they do.

The court will effectively render judgment on the leadership of the president. It was Obama who, at every turn during the original health-care debate, pressed for a more ambitious package that required Americans to purchase insurance.

A nullification would serve as a dramatic rebuke of that decision as well as the judgments Obama and his advisers made about the legality of the law.

“He’s mortgaged his presidency, at least his first term, on health care,” said George C. Edwards, the author of a new book on Obama called “Overreach” and a historian at Texas A&M University. The law “would have restructured a major aspect of life in America. It would have been a major, major legacy for the president. If that is thrown out, he has much less to show for it.”

Less clear are the short-term political implications of a Supreme Court decision to throw out the law. A number of allies of the measure, including Senate Majority Leader Harry M. Reid (D-Nev.), said it’s possible that such a ruling could help Obama’s reelection campaign by galvanizing Democratic voters.

These Democrats did not think the oral arguments went well for the president. But they see an opportunity to rally voters who are passionate about health-care reform — and to portray the Supreme Court as a partisan body.

“If they overturn the individual mandate and undermine the central element of this bill a few months before the election, it will anger Democrats and rile up the base,” said Neera Tanden, president of the left-leaning policy group Center for American Progress and a policy adviser to Obama’s 2008 campaign. “People will see it for what it is: an activist court rendering a partisan decision.”

One liberal group formed to build public support for the law, Protect Your Care, plans to throw out its playbook if the justices rule against the administration. Instead of promoting the popular provisions in the law, the group would devote its time in the fall to going negative on the court itself — painting the conservative justices as partisan ideologues who robbed Americans of needed benefits. The messages would be aimed at seniors who might lose prescription drug benefits and young people who might lose access to their parents’ health insurance plans.

“Since Bush v. Gore, from the progressive side, it would be the most galvanizing Supreme Court ruling ever,” said Eddie Vale, a spokesman for the group. “You’d have a 5-4 court, in clearly a partisan political decision, striking down not just President Obama’s biggest legislative accomplishment but also the biggest progressive legislation since LBJ.”

Romney’s role

Supporters of the law also think that Republican presidential front-runner Mitt Romney is in no position, because of his support as Massachusetts governor of a state-level individual mandate, to take political advantage if the statute is thrown out. If anything, they argue, such a ruling could prompt a discussion about whether Romney’s health-care overhaul, upon which Obama’s law was largely modeled, is unconstitutional.

“Romney does not have clean hands here,” said Rep. Gerald E. Connolly (D-Va.). “Saying that we stretched the commerce clause too much, and therefore it’s not constitutional — well, what about the law in Massachusetts that Mitt Romney signed? It has exactly the same premise.”

Connolly said there is no Plan B — no formal discussion on Capitol Hill or elsewhere on how to fix the Affordable Care Act if it is struck down. “Plans B, C, D and E were all considered during the debate and rejected for various and sundry reasons,” he said.

But that, too, could help Democrats — by placing the burden on Republicans to fix the health-care system themselves.

Republicans have said they could keep the law’s more popular provisions, such as barring insurers from denying coverage because of preexisting conditions. But supporters say it’s not possible to pay for that provision without requiring the 30 million Americans who are currently uninsured to purchase coverage.

Romney spokesman Ryan Williams said Wednesday that if the Supreme Court throws out the Affordable Care Act, conservatives will be galvanized to support Romney and prevent Obama from passing similar measures “that would have disastrous results for our country.”

Silence from Obama

One person not engaged in the fray is Obama himself. The president returned Tuesday from a four-day trip to South Korea, and since then, White House officials and campaign advisers at the team’s Chicago headquarters have officially refused to consider the possibility that the law could be rejected.

“There is no contingency plan that’s in place,” said deputy White House press secretary Josh Earnest. “We’re focused on implementing the law, and we are confident that the law is constitutional.”

The White House did defend Solicitor General Donald B. Verrilli Jr., who has come under scrutiny for his arguments before the Supreme Court this week.

And White House and campaign advisers are promoting the Affordable Care Act itself. Surrogates have fanned out across the country to highlight the law’s more popular elements, and over the past month, the campaign has sent about 1 million pieces of mail touting the law to women in battleground states. The campaign and the White House have even begun referring to the legislation as “Obamacare,” a derisive term coined by its detractors.

Allies speculated on several reasons that officials at the White House and in Chicago are cautious about speaking publicly on the Supreme Court case. One reason could be concern that any political talk from the campaign would inject a partisan flavor into the public discourse on a case that Obama advisers want the court to decide on its legal merits.

Another could be the legal view that the president, because of the Constitution’s mandate for the separation of powers, must not be seen as trying to influence a decision of the Supreme Court. That’s one likely reason, allies said, that Obama did not hold an event last week celebrating the two-year anniversary of the law’s signing — the date fell just three days before oral arguments began.

Those concerns also help explain the reluctance of some advisers — and allies such as Democratic National Committee Chairman Debbie Wasserman Schultz (Fla.), who declined to be interviewed on the subject — to speak openly about the matter.

With the case not likely to be decided before June, the caution is likely to continue.

Staff writers Rosalind S. Helderman, Peter Wallsten and Scott Wilson and polling manager Scott Clement contributed to this report.