In January 2001, CBO's baseline projections showed a cumulative surplus of $5.6 trillion for the 2002-2011 period. The actual results have differed from those projections because of subsequent policy changes, economic developments that differed from CBO's forecast, and other factors. As a result, the federal government actually ran deficits from 2002 through 2010 and will incur a deficit in 2011 as well. The cumulative deficit over the 10-year period will amount to $6.2 trillion, CBO estimates—a swing of $11.8 trillion from the January 2001 projections.
Worth a read.