WASHINGTON – In a momentous ruling touching virtually every American, the Supreme Court narrowly upheld President Barack Obama's historic health care overhaul Thursday with the unlikely help of conservative Chief Justice John Roberts.

But the decision also gave Republicans unexpected ammunition to energize supporters in the battle for the White House and to fight "Obamacare" as a new tax on people who don't obtain health insurance.

Roberts' vote, along with those of the court's four liberal justices, preserved the largest expansion of the nation's social safety net in more than 45 years, including the hotly debated core requirement that nearly everyone have health insurance or pay a penalty. The aim is to extend coverage to more than 30 million people who now are uninsured