America's historic health care overhaul, certain now to touch virtually every citizen's life, narrowly survived an election-year battle at the Supreme Court Thursday with the improbable help of conservative Chief Justice John Roberts.

But the ruling, by a 5-4 vote, also gave Republicans unexpected ammunition to energize supporters for the fall campaign against President Barack Obama, the bill's champion — and for next year's vigorous efforts to repeal the law as a new federal tax

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

The decision meant the huge overhaul, still taking effect, could proceed and pick up momentum over the next several years, with an impact on the way that countless Americans receive and pay for their personal medical care.