When it comes to spending cuts, Congress is looking in the wrong place. Most federal nondefense spending, other than Social Security and Medicare, is now done through special tax rules rather than by direct cash outlays. The rules are used to subsidize a wide range of spending including education, child care, health insurance, and a myriad of other congressional favorites.

These tax rules—because they result in the loss of revenue that would otherwise be collected by the government—are equivalent to direct government expenditures. That's why tax and budget experts refer to them as "tax expenditures." This year tax expenditures will raise the federal deficit by about $1 trillion, according to estimates by the congressional Joint Committee on Taxation. If Congress is serious about cutting government spending, it has to go after many of them....

If tax expenditures are not cut, taxes on households and businesses will have to rise to prevent an explosion of the national debt, which is now projected to increase to 90% of GDP by 2020 from today's 63%. When benefits for Social Security and Medicare are set aside, the rest of the outlay side of the budget is too small—7.5% of GDP—to provide much scope for reducing annual budget deficits that are now projected to average 5% of GDP for the rest of this decade. In contrast, total tax expenditures are now 6.4% of GDP.