Rare is the occasion when the nine justices of the U.S. Supreme Court gather to hear three days of arguments, and rarer still is when it is for a case like Obamacare — one that cuts to the core of the Constitution and whose outcome could fundamentally alter the role of the federal government and its power over the people. But today the Court will do just that when it open its doors and begins weighing the arguments on the constitutionality of President Barack Obama’s seminal health care law.