WASHINGTON -- The individual health insurance mandate is constitutional, the Supreme Court ruled Thursday, upholding the central provision of President Barack Obama's signature Affordable Care Act.

The controlling opinion, written by Chief Justice John Roberts, upheld the mandate as a tax, although concluded it was not valid as an exercise of Congress' commerce clause power. Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan joined in the outcome.

The decision in National Federation of Independent Business v. Sebelius comes as something of a surprise after the generally hostile reception the law received during the six hours of oral arguments held over three days in March. But by siding with the court's four Democratic appointees, Chief Justice Roberts avoided the delegitimizing taint of politics that surrounds a party-line vote while passing Obamacare's fate back to the elected branches. GOP candidates and incumbents will surely spend the rest of the 2012 campaign season running against the Supreme Court and for repeal of the law.

Five justices concluded that the mandate, which requires virtually all Americans to obtain minimum health insurance coverage or pay a penalty, falls within Congress' power under the Constitution to "lay and collect taxes."

"The individual mandate cannot be upheld as an exercise of Congress's power under the Commerce Clause," Roberts wrote. "That Clause authorizes Congress to regulate interstate commerce, not to order individuals to engage in it. In this case, however, it is reasonable to construe what Congress has done as increasing taxes on those who have a certain amount of income, but choose to go without health insurance. Such legislation is within Congress's power to tax."

Ginsburg, writing separately for the four liberals, said they would have upheld the mandate under the commerce clause too. "Unlike the market for almost any other product or service, the market for medical care is one in which all individuals inevitably participate," she wrote. "Virtually every person residing in the United States, sooner or later, will visit a doctor or other health care professional."

Justices Antonin Scalia, Anthony Kennedy, Clarence Thomas and Samuel Alito joined in a dissent. Together, Roberts' controlling opinion, Ginsburg's concurrence, the four-justice dissent and Thomas' own dissent add up to 187 pages.

In a nod to the importance of the health care cases, Roberts, Ginsburg and Kennedy all chose to read summaries of their opinions from the bench.

In a section of his opinion joined by the liberal justices, Roberts noted that the conservative dissenters contend that the mandate cannot be upheld as a tax "because Congress did not 'frame' it as such. In effect, they contend that even if the Constitution permits Congress to do exactly what we interpret this statute to do, the law must be struck down because Congress used the wrong labels."

But the majority was not persuaded by that argument. Roberts wrote that the mandate provision "need not be read to do more than impose a tax. That is sufficient to sustain it."

On Medicaid expansion, the court upheld the expansion but with a critical caveat: The federal government may not threaten the states that don't comply with the loss of their existing funding. Essentially, the Medicaid expansion is now optional for the states.

"As for the Medicaid expansion, that portion of the Affordable Care Act violates the Constitution by threatening existing Medicaid funding," Roberts wrote. "Congress has no authority to order the States to regulate according to its instructions. Congress may offer the States grants and require the States to comply with accompanying conditions, but the States must have a genuine choice whether to accept the offer. The States are given no such choice in this case: They must either accept a basic change in the nature of Medicaid, or risk losing all Medicaid funding. The remedy for that constitutional violation is to preclude the Federal Government from imposing such a sanction."

For their part, the dissenters were not impressed with Roberts' parsing of the law. "The Court regards its strained statutory interpretation as judicial modesty. It is not. It amounts instead to a vast judicial overreaching," wrote the four other conservatives.

They then looked to the political future: The majority's decision, they argued, "creates a debilitated, inoperable version of health-care regulation that Congress did not enact and the public does not expect. It makes enactment of sensible health-care regulation more difficult, since Congress cannot start afresh but must take as its point of departure a jumble of now senseless provisions, provisions that certain interests favored under the Court’s new design will struggle to retain. And it leaves the public and the States to expend vast sums of money on requirements that may or may not survive the necessary congressional revision."

Summarizing his delicate decision from the bench, Roberts reminded his listeners that it is "not our job to save the people from the consequences of their political choices." Still, the decision appeared to do just that.

By narrowing Congress' commerce and spending powers, Roberts moved the law in a decidedly conservative direction. Yet by invoking the taxing power, he saved not only the people but also Congress, the president and the Supreme Court itself from the consequences of their political choices that had seemed so evident at oral argument three months ago.

Careful legal parsing aside, the bottom line is: The Affordable Care Act has survived.

HuffPost readers: How will the Supreme Court's Affordable Care Act ruling affect your family? Tell us: offthebus@huffingtonpost.com (include your phone number if you are willing to be interviewed).

Erin Mershon contributed to this report.

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  • Round 1: The District Courts Divide

    U.S. District Judge George Caram Steeh, a Clinton appointee sitting in the Eastern District of Michigan, released the first major Affordable Care Act decision in October 2010. In <a href="http://www.mied.uscourts.gov/news/docs/09714485866.pdf" target="_hplink"><em>Thomas More Law Center v. Obama</em></a>, Steeh sided with the government to hold the law constitutional. "The decision whether to purchase insurance or to attempt to pay for health care out of pocket is plainly economic," Steeh wrote. "These decisions, viewed in the aggregate, have clear and direct impacts on health care providers, taxpayers and the insured population, who ultimately pay for the care provided to those without insurance."

  • Round 1: The District Courts Divide

    At the end of November 2010, another Clinton appointee, Judge Norman Moon of the Western District of Virginia, agreed with Judge Steeh. In <a href="http://www.vawd.uscourts.gov/OPINIONS/MOON/LIBERTYUNIVERSITYVGEITHNER.PDF" target="_hplink"><em>Liberty University v. Geithner</em></a>, Moon wrote that "by choosing to forgo insurance, plaintiffs are making an economic decision to try to pay for health care services later, out of pocket, rather than now, through the purchase of insurance."

  • Round 1: The District Courts Divide

    In December 2010, however, Judge Henry Hudson, a George W. Bush appointee sitting in the Eastern District of Virginia, ruled otherwise. In <a href="http://media.washingtonpost.com/wp-srv/metro/docs/Hudson_ruling.pdf?hpid=topnews" target="_hplink"><em>Virginia v. Sebelius</em></a>, Hudson struck down the individual mandate, writing that "an individual's personal decision to purchase -- or decline to purchase -- health insurance from a private provider is beyond the historical reach of the commerce clause." Importantly, Hudson also held that the individual mandate is severable from the rest of the Affordable Care Act, which means a court can strike it down while allowing the law's remaining provisions to stand.

  • Round 1: The District Courts Divide

    Finally in January 2011, Judge Roger Vinson, a Reagan appointee in the Northern District of Florida, evened the score but upped the ante. In <a href="http://www.scribd.com/doc/47905937/Health-Care-Ruling-by-Judge-Vinson" target="_hplink"><em>Florida v. Department of Health and Human Services</em></a>, not only did he strike down the individual mandate as exceeding Congress' power under the commerce clause, but he also took the whole health care law down with it. "The act," Vinson wrote, "like a defectively designed watch, needs to be redesigned and reconstructed by the watchmaker."

  • Round 2: The Appeals Courts Split

    In June 2011, the U.S. Court of Appeals for the 6th Circuit <a href="http://www.ca6.uscourts.gov/opinions.pdf/11a0168p-06.pdf" target="_hplink">upheld, by a 2-1 vote</a>, Judge Steeh's decision in <em>Thomas More Law Center</em>. Circuit Judge Jeffrey Sutton, a George W. Bush appointee, was the first judge chosen by a Republican president to reject the commerce clause challenge, writing that "no one must 'pile inference upon inference' to recognize that the national regulation of a $2.5 trillion industry, much of it financed through" national health insurance companies, "is economic in nature." He joined Judge Boyce Martin, a Jimmy Carter appointee, in the majority, while Judge James L. Graham, a Reagan appointee, wrote a vigorous dissent. In August, the 11th Circuit, reviewing <em>Florida v. HHS</em>, <a href="http://www.uscourts.gov/uscourts/courts/ca11/201111021.pdf" target="_hplink">produced a near mirror-image result</a>. Judge Frank Hull, a Clinton appointee, joined the Reagan-appointed Judge Joel Dubina to affirm District Judge Vinson's decision to strike down the individual mandate. Judge Stanley Marcus, a Clinton appointee, dissented, quoting heavily from Sutton's 6th Circuit concurring opinion. All three 11th Circuit judges found the mandate severable from the rest of the Affordable Care Act, reversing District Judge Hudson's decision to deep-six the entire law. Both appeals courts unanimously rejected the government's taxing power argument, insisting that if Congress had thought the penalty for not buying insurance was a tax, it would have explicitly called it a tax. On this issue, a third appeals court created another circuit split.

  • Round 2: The Appeals Courts Split

    In September 2011, the 4th Circuit dismissed two challenges to the health care law, finding that the plaintiffs did not have standing to bring their lawsuits. The panel did find that <a href="http://pacer.ca4.uscourts.gov/opinion.pdf/102347.P.pdf" target="_hplink">the penalty for not buying insurance was a tax</a> -- a good sign for the government's defense of the law. But rather than hold that the individual mandate was a valid exercise of Congress' taxing power, Judges Diana Gribbon Motz, a Clinton appointee, and James Wynn, an Obama appointee, said that another federal law, the Anti-Injunction Act, prevented the plaintiffs from challenging the mandate until they actually had to pay the tax -- which cannot happen before the provision goes into effect in 2014. The third judge, Obama appointee Andre Davis, said he wouldn't have dismissed the lawsuits and would have upheld the individual mandate based primarily on commerce clause ground. Regardless of the methodology, the Obama administration was now winning 2-1 in the courts of appeals against the Affordable Care Act's challengers.

  • Final Round: The Supreme Court Takes The Case

    The Supreme Court is most likely to choose to hear a case for one of three reasons: The constitutionality of a federal law hangs in the balance, the circuit courts disagree on the same issue, or the solicitor general advises the Court to take the case. Cases that fulfill just one of these considerations stand a good chance of reaching the justices. The health care cases had all three. In November 2011, the justices <a href="http://www.huffingtonpost.com/2011/11/14/obama-health-care-law_n_1092387.html" target="_hplink">agreed to review</a> the 11th Circuit's decision. To signal how seriously it took the challenges, the Court soon thereafter scheduled six hours of oral argument to take place from March 26 to 28, 2012. Normally, even for blockbuster cases, the justices only allot one hour for oral argument.

  • Final Round: The Supreme Court Hears Oral Argument

    All eyes turned to the Supreme Court in late March 2012 when the justices heard oral argument and gave their first public hints of where they stood on the Affordable Care Act's constitutionality. On the first day, March 26, liberal and conservative justices alike <a href="http://www.huffingtonpost.com/2012/03/26/health-care-law-supreme-court_n_1373455.html" target="_hplink">showed little interest</a> in following the 4th Circuit's decision to throw out the challenge to the health care law on a technicality before ever reaching the constitutional merits of the individual mandate. That display of unity disappeared on Tuesday, March 27, as the Court took on the <a href="http://www.huffingtonpost.com/2012/03/27/supreme-court-health-care_n_1373469.html" target="_hplink">main event</a>: two hours of argument over the mandate. The Court's four Democratic appointees all appeared to find the mandate well within Congress' powers to regulate interstate commerce, as the 6th Circuit had held; the Court's five Republican appointees, in concert with the 11th Circuit, seemed to think otherwise. Only in the final moments did swing vote Justice Anthony Kennedy soften his tone by musing aloud whether the health insurance market is different enough, after all, to allow a mandate to prevent cost-shifting where it might not be permissible in another market. "[M]ost questions in life are matters of degree," he said. On Wednesday, March 28, the justices <a href="http://www.huffingtonpost.com/2012/03/28/health-care-case-supreme-court-john-roberts_n_1386692.html" target="_hplink">considered</a> what other parts of the Affordable Care Act would fall if they found the mandate unconstitutional. No majority emerged. Several justices agreed with the challengers that the whole law must fall. Several others agreed with the Obama administration that two key (and popular) provisions could not survive without the mandate. Still others indicated some sympathy for severing the mandate alone and allowing the rest of the law to stand. A decision is expected by the end of June.