WASHINGTON — As the Obama administration presses ahead with the health care law, officials are bracing for the possibility that a federal judge in Virginia will soon reject its central provision as unconstitutional and, in the worst case for the White House, halt its enforcement until higher courts can rule.
..

The novel question before the courts is whether the government can require citizens to buy a commercial product like health insurance. Because the Supreme Court has said the commerce clause of the Constitution allows Congress to regulate “activities that substantially affect interstate commerce,” the judges must decide whether the failure to obtain insurance can be defined as an “activity.