source: CBO, January 26, 2011, at 57
The CBO explains (at 56):
Compared with outlays over the past 40 years, the biggest difference in federal spending relative to GDP in the coming decade will be the amount of mandatory spending. In CBO’s baseline projections, mandatory spending averages 13.2 percent of GDP over the coming 10 years, in contrast to the 9.9 percent of GDP it averaged from 1971 to 2010 (see Figure 3-1). That higher level of spending is mostly a result of outlays for Social Security, Medicare, Medicaid, and other health programs, which are projected to grow from 10.3 percent of GDP in 2012 to 12.7 percent in 2021.Social Security spending's turned to deficit, and Medicare's "a true fiscal nightmare." More evidence that the problem is entitlements, not, say, defense. And, the CBO "understate[s] the gravity of our situation."
(via Instapundit, MaxedOutMama)