From the Summary: "Americans often mention economic issues as the most important problem facing the United States. Recent economic issues mentioned include rising gasoline prices, rising unemployment, falling home prices, and rising mortgage interest rates. An increasing proportion of Americans mention large deficits as a major concern. Many policy makers and analysts rate long-term federal budgetary problems high on their list of economic problems facing the United States. For example, President Obama's bipartisan fiscal commission, in December 2010, recommended reducing deficits by nearly $4 trillion over the next 10 years. Budget experts from think tanks and academia have developed proposals for dealing with longterm fiscal difficulties. Many argue that the federal budget deficits are unsustainable and threaten the future of the economy, but they differ on the causes of federal deficits. […] Estimates of the revenue losses and distributional effects of tax expenditures depend on the parameters of the tax code. Both will change not only because of direct changes to the tax expenditures themselves, but also because of changes elsewhere in the tax code. Consequently, while many tax expenditures may be considered permanent, the revenue losses can vary year to year because of changing economic conditions and changes to the tax code. "
CRS Report for Congress, RL34622