The United States Supreme Court has upheld Barack Obama's landmark overhaul of the country's healthcare system, handing the president a historic victory and bolstering his chances in a close re-election race this November.
The five-to-four decision handed down on Thursday, led by conservative Chief Justice John Roberts, upheld the mandate that individuals who can afford to buy insurance must do so - the key tenet of the act.
But the court arrived at its decision in an unexpected fashion, deciding that Congress could not mandate individuals to buy insurance but could rather apply a penalty tax to those who do not.
Roberts supported the law's constitutionality on those grounds, while the four justices opposed to the decision argued the law should be struck down entirely.
The decision means that two years after Obama signed the Patient Protection and Affordable Care Act - which aims to insure 32 million additional people and prevent coverage from being refused because of medical history - its key tenet thinly survived at the hands of a chief justice whose nomination Obama opposed when he was a senator.
| Al Jazeera's Cath Turner speaks to patients at a community health center in Buffalo, New York
"Today the Supreme Court ... upheld the principle that people who can afford health insurance should take the responsibility to buy health insurance," Obama said after the ruling.
Taking aim at Mitt Romney, the former Massachusetts governor who is running against Obama for the presidency, and says he will repeal the law if he wins, Obama pointed out that his Republican opponent had supported the same mandate when he reformed healthcare in his state.
"We can't refight the political battles of the past two years," Obama said of the virulent protests against the law that erupted in many states.
"I'm as confident as ever that when we look back five years from now, 10 years from now or 20 years from now, we'll be better off because we had the courage to pass this law."
Although the US is the world's largest economy, it is the only industrialised democracy that does not provide health care coverage to all its citizens.
'Get rid of Obama'
Romney, in brief remarks to reporters before the president spoke, called the act "bad law" that hinders job growth, raises taxes by $500bn and adds to the national debt.
| Romney said businesses would now be less likely to hire new employees [Reuters]
He alleged that the act would force 20 million people with insurance to change their plans, something Obama has denied, and said businesses would be less likely to hire new employees.
"This is a time for the American people to make a choice," Romney said.
"You can choose whether you want a larger and larger government, a higher deficit, whether you're willing to have a plan that causes you to lose insurance that you like, or whether you want to return to a time where you can make your own decisions.
"If we want to get rid of Obamacare, we have to get rid of President Obama."
Al Jazeera's Patty Culhane, reporting from Washington, said the court's decision was "the final hurdle" for Obama's signature piece of legislation.
Opponents of the act must now hope for a Republican president and Congress to be elected in November, setting the stage for repealing the act, or voting away its funding, before most of the provisions take effect over the coming years, she said.
The law is extremely complex, and polls indicate a majority of Americans disapprove of it, Culhane said.
Jonathan Cohn, an appellate lawyer at Sidney & Austin who has clerked for the court, told Al Jazeera the mechanics of the decision were unexpected.
"The president did not want to call it a tax, but nonetheless the court says it's a tax, we're going to uphold it," he said.
Cohn noted that the justices had also dealt Obama a setback.
The administration's lawyers had argued that states that did not want to opt into the new healthcare system should lose all of their government health subsidies, known as Medicaid, as leverage to force them to participate.
But the court on Thursday said that cutting off such funds was unconstitutional.
Instead, a majority decided that states that accepted new government money to run the expanded health care programmes would be forced to abide by all the new provisions, and those that wanted to opt out would be unchanged.
Democrats welcomed the ruling, while Republicans warned that they would try to repeal it.
"Now that the matter is settled, I hope that we can work together to create jobs and secure this country's economic future," wrote Senator Majority Leader Harry Reid on Twitter.
The Senate's Republican leader, Mitch McConnell, told CBS News that Congress "must act to repeal this misguided law".
McConnell said it "limited choices and increased health care costs for American families, [and] it has made it harder for American businesses to hire".
Al Jazeera's Kimberly Halkett, reporting from Washington, said the dueling statements framed the biggest political debate heading into the presidential election.
"I expect you're going to hear that a lot now," she said, noting that the House of Representatives had set a July 9 vote to attempt, likely only symbolically, to repeal the act.