Supporters of the 2009 Patient Protection and Affordable Care Act (ACA) — so-called Obamacare — have high hopes that when fully implemented, the sweeping reform measure will reduce medical costs and make millions of currently uninsured Americans eligible for health care coverage. But four years after its passage, the law continues to face legal, political and ideological challenges. Conservative Republicans argue that it imposes federal control over medical decisions, and some religiously affiliated employers object to the law’s mandate that preventive-health coverage include contraceptives. Meanwhile, many GOP-led states, especially in the South, are balking at expanding coverage for poor and disabled people under Medicaid, as is urged — but not required — under the law. And some small businesses say expanding health coverage to their workers would be too costly.