Medicare, the national health-insurance plan for the elderly and disabled, is much like Social Security in terms of the people it serves, its popularity and its fragile future -- except that it's in much worse shape financially. The program serves 42 million Americans and costs more than $325 billion per year, nearly 13 percent of the federal budget. But current projections say Medicare will be unable to cover its bills by 2019 -- long before Social Security, which should be able to cover its costs until 2041.