One year ago, President Obama signed into law sweeping changes to the nation’s health care system. The Patient Protection and Affordable Care Act re-organized a sector that accounts for one-sixth of the national economy. Some of its more popular elements have already kicked in. Insurance companies can no longer deny coverage to children with pre-existing conditions. And some preventative treatments are now free. But the law faces threats. In a mostly symbolic vote, the GOP-controlled House voted to repeal the Act as one of its first actions. And portions of it could be overturned by the Supreme Court. Health and Human Services Secretary Kathleen Sebelius on the health care overhaul law.