WASHINGTON (AP) - The Supreme Court has upheld the heart of President Barack Obama's health care overhaul -- ruling in favor of the requirement that most Americans can be required to have health insurance, or else pay a penalty. The decision means the historic overhaul will continue to take effect over the next several years, affecting the way countless Americans receive and pay for their personal medical care. The ruling also hands President Barack Obama a campaign-season victory. The court found problems with the law's expansion of Medicaid. But even there, it said the expansion could proceed as long as the federal government does not threaten to withhold the entire Medicaid allotment to states if they don't take part in the extension. The court's four liberal justices, Stephen Bryer, Ruth Bader Ginsburg, Elena Kagan and Sonia Sotomayor, joined Roberts in the outcome.