According to a report from the Government Accountability Office [GAO], the federal government's long-term fiscal outlook is unsustainable--the growing imbalance between revenues (money collected) and spending (driven by health care, Social Security, and net interest on the debt). Absent policy changes, the debt-to-GDP ratio would surpass its historical high of 106 percent within 15 to 25 years.
The report can be obtained at http://www.gao.gov/assets/690/684454.pdf.