http://www.epi.org/publications/entry/social_security_and_the_federal_deficit/
(Updated August 9, 2010, 3:00pm)
The conventional wisdom in Washington is that an aging population will cause entitlement spending to balloon, driving our nation deeply into debt (see, for example, Brookings-Heritage Fiscal Seminar 2008, Peterson-Pew Commission 2009). While it is true that Medicare spending will soar if health care cost growth is not brought under control, the same is not true of Social Security spending, which is projected to level off as a share of GDP after the Baby Boomer retirement.
Social Security is running a surplus of $77 billion this year and amassing a trust fund large enough to last through the peak retirement years of the Baby Boomers. Social Security can only spend what it receives in tax revenues and has accumulated in its trust fund from past surpluses and interest earnings. It cannot add to the deficit if the trust fund is exhausted because the law prohibits it from borrowing (if current revenues and savings in the trust fund are not sufficient to pay promised benefits, these have to be cut). Though modest changes will be needed to put Social Security in balance over the 75-year planning period, the projected shortfall is less than 1% of gross domestic product (GDP).