The Supreme Court upheld the centerpiece of President Barack Obama’s health care law Thursday, ruling that Congress did not overstep its power by requiring nearly all Americans to buy health insurance.

Chief Justice John Roberts joined with the court’s four liberal justices in the ruling, which says Congress had the authority to impose the law’s individual mandate under Congress’s taxing power.

The ruling is a surprise victory for the Obama administration, which faced tough questions from the court during the oral arguments in March.

"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."

"The federal government may enact a tax on an activity that it cannot authorize, forbid or otherwise control,” Roberts wrote.

The court has issued a more complex ruling on Medicaid, and it is not yet clear that the entire health law has been upheld.

This article first appeared on POLITICO Pro at 10:19 a.m. on June 28, 2012.