Its $2.15 trillion for 2003 according to the CBO.
http://www.cbo.gov/showdoc.cfm?index=1821&sequence=0#table1I think John Ford is right in saying that GDP includes government spending and they definitely don't tax themselves.
THE GDP for 2003 was $10.98 trillion. Deduct govt spending of 2.15 trillion. That leaves $8.83 trillion taxable money. You need to take about 24% in sales tax to fund the current level of spending. (Think what that would do to the price of a $200,000 new home!) Although at that level the sales tax would eliminate the need for personal income tax, payroll tax, corporate tax and all other federal taxes. It would also eliminate the deficit.
The bottom line is government spends way too much and the only chance of getting its spending reduced to an acceptable level is to elect Badnarik.