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In a victory for President Obama, the Supreme Court decided to uphold his signature health care law's individual mandate in a split decision, upending speculation after hostile-seeming oral arguments in March that the justices would overturn the law. The mandate has been upheld as a tax, according to SCOTUSblog, with Chief Justice John Roberts joining the liberal wing of the court.

Twenty six states sued over the law, arguing that the individual mandate, which requires people to buy health insurance or face a fine starting in 2014, was unconstitutional. Opponents cast the individual mandate as the government forcing Americans to enter a market and buy a product against their will, while the government countered that the law was actually only regulating a market that everyone is already in, since almost everyone will seek health care at some point in his or her life.

Before oral arguments in March, polls of Supreme Court experts and scholars showed that most believed the mandate would be upheld as an exercise of Congress' power to regulate interstate commerce. But after justices seemed deeply skeptical of the mandate in oral arguments in March, the consensus flipped, with most experts guessing the court would strike down the law.

House Republicans have vowed to repeal the entire law, though it's unlikely the Democratic-controlled Senate would let that happen.

Though the sweeping, 1,000-page plus law passed more than two years ago, much of it will not go into effect until 2014. That's when states will have to set up their own health insurance exchanges, Medicaid will be expanded by 16 million low-income people, and Americans will have to buy health insurance (for many, with a government subsidy) or pay a penalty of 1 percent of their income to the IRS. Employers who have more than 50 employees and don't offer insurance will also begin to face a penalty. Insurers will no longer be able to turn away people with preexisting conditions, or charge people higher premiums based on their gender or health.

Only about 6 percent of the population will actually be required to buy health insurance or face a tax under the mandate, since most people already have coverage or will get it through Medicare, according to the Urban Institute.

Many of the more popular provisions of the law have already gone into effect, including a regulation saying insurers have to let children stay on their parents' plans until they are 26 years old, which 2.5 million Americans have already taken advantage of. Insurers can also no longer turn away children with preexisting conditions, and sick uninsured people can buy coverage in high-risk pools set up by the government.