The Obama administration got an enormous victory on Thursday when the Supreme Court voted 5-4 to uphold the President’s signature achievement: the 2010 health care law.

And in a surprise to many court watchers, it was Chief Justice John Roberts who sided with the more liberal justices and wrote the majority opinion.

The central issue in the case was whether the individual mandate, which requires that all Americans must buy health insurance or face a penalty, was constitutional. Roberts wrote the mandate is not a valid exercise of Congress’ power to regulate commerce, but is a valid use of its taxing power.

“Simply put, Congress may tax and spend,” Roberts wrote in the majority opinion. “This grant gives the federal government considerable influence even in areas where it cannot directly regulate.”

In addition, the Court limited a massive expansion of Medicaid, the federal program that provides health care to the poor, but did not strike it down.

Many congressional Republicans expected the court to strike down at least some parts of the law, and have now vowed to renew their efforts to repeal it.

[MSNBC]