Bruce Bartlett: The Fiscal Legacy of George W. Bush - NYTimes.com: In January 2001, the office projected that the federal government would run a total budget surplus of $3.5 trillion through 2008 if policy was unchanged and the economy continued according to forecast. In fact, there was a deficit of $5.5 trillion.
The projected surplus was primarily the result of two factors. First was a big tax increase in 1993 that every Republican in Congress voted against, saying that it would tank the economy. This belief was wrong. The economy boomed in 1994, growing 4.1 percent that year and strongly throughout the Clinton administration.
The second major contributor to budget surpluses that emerged in 1998 was tough budget controls that were part of the 1990 and 1993 budget deals. The main one was a requirement that spending could not be increased or taxes cut unless offset by spending cuts or tax increases. This was known as Paygo, for pay as you go.