Further increases in federal debt relative to the nation’s output almost certainly lie ahead if current policies remain in place. The aging of the population and rising costs for health care will push federal spending, measured as a percentage of GDP, well above the levels experienced in recent decades. Unless policymakers restrain the growth of spending, increase revenues significantly as a share of GDP, or adopt some combination of those two approaches, growing budget deficits will cause debt to rise to unsupportable levels, as shown in the figure below. (For more details, see CBO’s recent report The Long-Term Budget Outlook.)
Although deficits during or shortly after a recession generally hasten economic recovery, persistent deficits and continually mounting debt would have several negative economic consequences for the United States. Some of those consequences would arise gradually—but a high level of federal debt, combined with an unfavorable long-term budget outlook, would also increase the probability of a sudden fiscal crisis prompted by investors’ fears that the government would renege on the terms of its existing debt or that it would increase the supply of money to finance its activities or pay creditors and thereby boost inflation. The resulting abrupt rise in interest rates would create serious challenges for the U.S. government. For example, a 4-percentage-point across-the-board increase in interest rates would raise federal interest payments next year by about $100 billion; if those higher rates persisted, net interest costs in 2015 would be nearly double the roughly $460 billion that CBO currently projects for that year. Such an increase in rates could also precipitate a broader financial crisis because it would reduce the market value of outstanding government bonds, inflicting losses on mutual funds, pension funds, insurance companies, banks, and other holders of federal debt.
From the blog of the Director of the Congressional Budget Office
Our National credit card is maxed out, and we aren't even making minimum payments.