WASHINGTON (Reuters) – In the end, it all came down to Chief Justice John Roberts, the sphinx in the center chair, who in a stunning decision wove together competing rationales to uphold President Barack Obama’s healthcare plan.

Roberts’ action instantly upended the conventional wisdom that he would vote with his four fellow conservative justices on the US Supreme Court and undercut the agenda of a Democratic president, who as a senator in 2005 had opposed Roberts’ appointment to the bench.

On Thursday, the US Supreme Court upheld much of President Obama’s controversial Affordable Care Act — health care reform — in a 5 to 4 decision that was sure to upset many Americans regardless of what it was.

But Thursday’s extraordinary conclusion to the bitterly fought healthcare battle was quite ordinary in some ways.

Roberts hewed to a traditional Supreme Court principle that if the justices can find any constitutional grounds on which to uphold a law, they should do so.

The 57 year old chief justice also followed a stated principle of his own: narrowly deciding cases and trying to preserve the integrity of the judiciary in polarized Washington.

While he has voted consistently with the conservative bloc on social issues, such as abortion rights and racial policies, Roberts in his public remarks has suggested that he seeks, as chief, to transcend an ideological label.

He routinely refers to the court’s place in history and has bristled at polls and public commentary that suggest the high court acts in the same political realm as the two elected branches of government.

Tom Goldstein, founder of SCOTUSblog — a respected website on the High Court — says Roberts followed the law, but knew he was making history.

Indeed, in his comments during oral arguments in the healthcare case, Roberts hinted that he could be open to siding with the government.

He expressed concern that the court over which he presides might be seen as ignoring more than 75 years of precedent and rolling back US law to the New Deal era.

The last time the Supreme Court struck down a major act of Congress was in 1936, when the court invalidated a federal law that limited work hours and prescribed minimum wages for coal workers.

“He is positioning the court as the one, competent, principled institution in Washington,” said Pamela Karlan, a Stanford University law professor.

Almost every conservative scholar in the country is now asking: What happened to the Chief Justice.

DEFYING HISTORYAs the lone conservative standing with four liberals, Roberts defied recent history, most people’s expectations, and the deepest held hopes of the right wing and Tea Party opponents of the law.

He also rejected the prevailing view of Republican politicians, who had been his strongest backers when President George W.

“The court avoided, despite an enormous amount of pressure to invalidate this law, staining itself as excessively partisan,” said Bradley Joondeph, a law professor at Santa Clara University.

“Think of the people who supported Chief Justice Roberts, who put him on the court, who were rooting for him.”.

On the Roberts court, the swing vote role has often been played by Justice Anthony Kennedy, not the chief himself.

For example, Kennedy, a conservative appointed to the court by President Ronald Reagan in 1988, was crucial to its 1992 decision to uphold the right to abortion.

Thursday’s case marked the first time that Roberts joined the liberal bloc as the deciding fifth vote in a major case.

On Thursday, Kennedy fell in with the conservatives and read their joint dissent.

“The court regards its strained statutory interpretation as judicial modesty,” Kennedy wrote.

He rejected the Obama administration’s main argument that the core of the law, a mandate that requires most Americans to buy health insurance by 2014 or face a penalty, was covered by Congress’s power to regulate interstate commerce.

Concluding that the mandate “cannot be sustained under a clause authorizing Congress to ‘regulate commerce,’” the chief justice even went so far as to raise the hypothetical “broccoli” mandate—a pet issue of the mandate’s opponents that was raised by Justice Antonin Scalia at the oral arguments for the case in March.

Roberts said that power, while broad, does not extend to “inactivity,” such as the choice not to buy insurance.

Upholding the Affordable Care Act under the Commerce Clause would give Congress the same license to regulate what people do not do.

In their briefs and arguments, both sides characterized the health insurance mandate as distinctive, and it is unclear whether another Congressional regulation could be struck down under the Roberts “inactivity” rationale.

Roberts’ judgment on the Commerce Clause issue was endorsed by fellow conservatives Kennedy, Antonin Scalia, Samuel Alito and Clarence Thomas.

But in turning to another constitutional ground on which to uphold the mandate, Congress’ taxation power, Roberts embraced the Obama administration’s secondary argument – and delivered a victory to the President.

And yet, on the Affordable Care Act, he was the swing vote that gave the Obama administration the victory, upholding the individual mandate as a tax.

Roberts reasoned that even though Congress had shied away from calling the penalty for not buying insurance a “tax,” it effectively is one.

As he read excerpts from the momentous decision Thursday, Roberts seemed to downplay the drama of the morning.

Among them was Justice John Paul Stevens, a liberal who had served with Roberts until he retired two years ago at the age of 90.

Following the usual decorum in the white marble and crimson draped room, the nearly 300 people listening to the chief justice gave no audible response.

Sean Brierley is a business journalist based in Hobart, Australia. Sean has a passion for financial markets and breaking news stories and loves writing about business news, stock market, and economic opinions that matters most to its audience. Sean spends a lot of time discovering and researching latest financial markets and industry news stories in order to make sure the latest and greatest stories are brought to you first on BigBoardNews.com.