By Matt Negrin and Ariane De Vogue

In a landmark ruling with wide-ranging implications, the Supreme Court today upheld the so-called individual mandate requiring Americans to buy health insurance or pay a penalty, the key part of President Obama’s signature health care law.

The court ruled 5 to 4, wiith Chief Justice John Roberts siding with the majority, that the mandate is unconstitutional under the Constitution’s commerce clause, but it can stay as part of Congress’s power under a taxing clause. The court said that the government will be allowed to tax people for not having health insurance.

“The Affordable Care Act’s requirement that certain individuals pay a financial penalty for not obtaining health insurance may reasonably be characterized as a tax,” Chief Justice John Roberts wrote in the ruling. “Because the Constitution permits such a tax, it is not our role to forbid it, or to pass upon its wisdom or fairness.”

In a speech today, Obama said from the White House that he wanted to move on, even as House Republicans vowed to vote symbolically to repeal it, and as his main opponent argued that the best way to ditch the law is to kick Obama out of office.

“The highest court in the land has now spoken,” Obama said. “We will continue to implement this law. And we will continue to improve on it where we can.”

Obama insisted that the debate over the political benefits from the court’s ruling “completely misses the point.”

“It should be pretty clear by now that I didn’t do this because it was good politics,” he said. “I did it because I believed it was good for the country.”

The ruling is a clear victory for the Obama administration and a defeat for Republicans, who had anticipated that at least some of the law would be struck down. But it also means the debate will continue.

“It actually settles nothing. By shifting the debate to the tax arena, and with a four-justice dissent, the decision guarantees only that the broader fight over a suitable national health policy will continue,” said Richard Saltman, a professor at the Rollins School of Public Health, Emory University. “In effect, the court decided this was too hot to handle. The focus will (has already) shift back to the political arena, where a deeply divided electorate will have to decide which policy path they want the country to pursue.”

The court’s ruling upholding the main part of Obama’s law means that people must buy health insurance or pay a tax up to several thousand dollars a year. Other popular provisions of the law will stay, including:

— If you are under 26, you can get health insurance from the plan your parents use. — If you’re on Medicare, you can get free mammograms. — If you have what’s called a pre-existing condition, you can get health insurance. — Insurance companies can’t deny you coverage even if you get sick or make a mistake on your health insurance application.

Watch: Obamacare ruling is bad law, says Mitt Romney.

The vote from the high court was five to four. Roberts, who was appointed by George W. Bush, joined the more liberal four justices in upholding the mandate. Justice Anthony Kennedy was thought to be the swing vote, but he sided with the conservative bloc.

“Our precedent demonstrates that Congress had the power to impose the exaction in section 5000 A under the taxing power and that section 5000 a need not be read to do more than impose a tax,” Roberts wrote.

Read the court’s full decision.

Pundits sailed off statements all morning espousing their views. From supporters:

“By authoring an opinion joined by the more liberal justices, upholding the so called individual mandate, Chief Justice Roberts has helped to strengthen the American Public’s faith in the Court as an impartial institution of Justice,” said Elizabeth Wydra, the chief counsel to the Constitutional Accountability Center, who supports the law. “The court today has affirmed the federal government’s constitutional power to provide national solutions to national problems.”

From the opposition: “I am disappointed with today’s Supreme Court decision because the court has cleared the way for what looks like a very broad use of the tax power. But we can still be very thankful that the court has defended the contours of the commerce clause,” said Carrie Severino of the Judicial Crisis Network.

Reading the dissent from the bench, Kennedy said the Affordable Care Act is invalid in its entirety.”

“It is true that if an individual does not purchase insurance, he or she affects the insurance market to a degree,” he said. “But the Government’s theory would make one’s mere existence the basis for federal regulation. There would be no structural limit on the power of Congress. As a result, the Government’s theory would change the relation between the citizens and the Federal Government in a fundamental way.”

Lyle Denniston, a Supreme Court expert who writes on the influential Scotus Blog, noted that the White House’s main argument failed — but that its Plan B case won out.

“Essentially, a majority of the court has accepted the Administration’s backup argument that, as Roberts put it, ‘the mandate can be regarded as establishing a condition — not owning health insurance — that triggers a tax — the required payment to IRS,'” he wrote. “Actually, this was the Administration’s second backup argument: first argument was Commerce Clause, second was Necessary and Proper Clause, and third was as a tax. The third argument won.”

The ruling has immediate effects on the presidential race. Obama has called his health care law “the right thing to do,” even as polling has determined that the law is unpopular. Mitt Romney, meanwhile, had vowed to repeal “ObamaCare” as soon as he became president, despite championing remarkably similar legislation as the governor of Massachusetts.

Even Karl Rove, the GOP uber-strategist who founded an outside spending group to defeat Obama in 2012, said the ruling helps Obama.

“If this is actually the decision, it’s a boost for the president, but it doesn’t make the controversy go away,” Rove said on Fox News. “In fact, it probably enhances the controversy.”

Reacting two hours after the ruling was handed down, Romney repeated his pledge to repeal the law on the first day of his would-be presidency.

“If we want to get rid of ObamaCare, we’re going to have to replace President Obama,” he said.

Obama was expected to make a statement within the hour.

While just 36 percent of people in the most recent ABC News/Washington Post poll had a favorable opinion of the health law, a similarly low number of people — 39 percent — had a favorable opinion of the health care system as it stands now. And while the GOP has trumpeted polling that shows Americans unsatisfied with the law as a whole, the White House has boasted of surveys that show that people are warmer to individual parts of the law, like letting young adults stay on their parents’ plans until they’re 26 and barring insurers from denying coverage to people with so-called pre-existing conditions.

Obama’s opponents in Congress signaled they aren’t done fighting. The Senate minority leader, Mitch McConnell, said that “Congress must act to repeal this misguided law.”

“Today’s decision does nothing to diminish the fact that Obamacare’s mandates, tax hikes, and Medicare cuts should be repealed and replaced with common-sense reforms that lower costs and that the American people actually want,” he said. “It is my hope that with new leadership in the White House and Senate, we can enact these step-by-step solutions and prevent further damage from this terrible law.”

The conservative Chamber of Commerce also chimed in. Said President Thomas Donohue: “While we respect the Court’s decision, today’s Supreme Court ruling does not change the reality that the health care law is fundamentally flawed. Left unchanged, it will cost many Americans their employer-based health insurance, undermine job creation, and raise health care costs for all.”

New Jersey Gov. Chris Christie said: “I’ve been clear from the very beginning that I do not believe a one-size-fits-all health care program works for the entire country and that each governor should have the ability to make decisions about what works best for their state. Today’s Supreme Court decision is disappointing and I still believe this is the wrong approach for the people of New Jersey who should be able to make their own judgments about health care. Most importantly, the Supreme Court is confirming what we knew all along about this law – it is a tax on middle class Americans.”

In court, the government argued that the health care law was passed partly because in 2009, 50 million people lacked health insurance. Costs of the uninsured were spiraling out of control and were being shifted to those who are insured, doctors and insurance companies. And, people with so-called pre-existing conditions were being denied coverage. The law offered insurance reforms but mandated that almost every American buy health insurance by 2014.

The government said that Congress was well within its authority to pass the individual mandate under the Commerce Clause and the Necessary and Proper Clause of the Constitution. As a secondary argument the government also said Congress had the authority to pass the mandate under its taxing authority.

Opponents — 26 states, an independent business group and two private citizens — said that while Congress has the authority to regulate interstate commerce, it doesn’t have the power to require people to buy a product. The opponents argued that the claim of federal power was both “unprecedented and unbounded.”

In March, the court devoted more than six hours of arguments to different aspects of the law.