The U.S. Supreme Court handed President Barack Obama a major victory Thursday, upholding the key part of his controversial health care plan in a 5-4 decision.

The so-called “individual mandate” requires Americans to have health insurance or face a financial penalty. U.S. Chief Justice John Roberts sided with the court's more liberal justices, writing in his majority opinion that “because the Constitution permits such a tax, it is not [the court's] role to forbid it, or to pass upon its wisdom or fairness.''

Justices Stephen Breyer, Ruth Bader Ginsburg, Elena Kagan and Sonia Sotomayor voted with Roberts to uphold the law.

President Barack Obama hailed the ruling as a victory “for people all over this country whose lives will be more secure because of this law and the Supreme Court's decision to uphold it.” He also said the court decision reaffirmed that in the United States, the wealthiest nation on Earth, no illness or accident should lead any family to financial ruin.

Mr. Obama's expected challenger in the 2012 election, Republican Mitt Romney, promised to repeal the law on his first day in office, if elected. He said “Obamacare was bad policy yesterday. It's bad policy today,” and warned the law will cause up to 20 million Americans to lose health care coverage they like or want to keep while also killing badly needed jobs.

The Obama administration had argued the “individual mandate” is valid under the U.S. Constitution because all Americans will need medical care at some point in their lives, and there is no practical alternative to insurance.

Twenty-six states filed suit against the reform law, contending that individuals cannot be forced to buy insurance, a product they may neither want nor need.

Republican lawmakers were quick to respond to the court decision, using it to launch a renewed effort to repeal the law in its entirety.

The Speaker of the House of Representatives, John Boehner, told reporters the court's ruling underscored the urgency to act.

He said, “There's a lot of resolve amongst our colleagues and amongst the American people to stop a law that's hurting our economy, driving up the cost of health care and making it more difficult for employers to hire new workers.”

U.S. Senate Republican leader Mitch McConnell also lashed out at the law, saying it “made the problems it was meant to solve even worse – the supposed cure has proven to be worse than the disease.”

The U.S. business community is also speaking out.

U.S. Chamber of Commerce President Thomas Donohue said his pro-business group still feels the health care law is fundamentally flawed. If left unchanged, he said, “it will cost many Americans their employer-based health insurance, undermine job creation, and raise health care costs for all.”

Still, the president's supporters applauded the ruling, hoping it will help lead to Democratic victories in the upcoming election.

The top Democrat in the House of Representatives, Nancy Pelosi, called the court ruling a victory for the American people because it “ensured health care would be a right for all, not a privilege for the few.”

Thursday's decision drew a large and energetic crowd to the steps of the Supreme Court, with students, parents, priests and even some belly dancers anxiously awaiting the decision. But the ruling – a complex look at the constitutionality of the Obama health care law – sparked confusion. Many in the crowd — and some in the news media — were at first not clear about what the decision meant.

The law passed in early 2010 is the signature piece of President Obama's legislative agenda during his time in office. It is intended to address rising health care costs and the financial problems many Americans have faced in trying to obtain health insurance.

But it's not just that the promises of this law weren't kept, it's that it made the problems it was meant to solve even worse – the supposed cure has proven to be worse than the disease.”

“The president of the United States himself promised up and down that this bill was not a tax. This is one of the Democrats' top selling points, because they knew it would have never passed if they said it was a tax.”