Government Spending and Taxation
This graph, showing government outlays and revenues as a percentage of GDP, is taken from the Congressional Budget Office's The Budget and Economic Outlook: An Update, August 2006. From the CBO's analysis:
Spending on Social Security, Medicare, and Medicaid is projected to grow rapidly during the 10-year period covered by CBO’s baseline (see Summary Figure 2); the resulting budgetary pressures will intensify in later years as the baby-boom generation ages and health care costs continue to rise. The percentage of the population age 65 or older will continue to increase (from 14 percent in 2016 to more than 19 percent in 2030). In addition, health care costs are likely to keep growing faster than GDP, as they have over the past four decades. As a result, spending for Social Security, Medicare, and Medicaid will exert pressures on the budget that economic growth alone is unlikely to alleviate. Consequently, substantial reductions in the projected growth of spending and perhaps a sizable increase in taxes as a share of the economy will probably be necessary to maintain fiscal stability in the coming decades.
You can find links to the CBO's reports, as well as data from the other federal agencies, at NABE's Macro Data and Links page.