Where the debt came from.

From The Great Debt Shift, from the non-partisan Pew Charitable Trusts:

In January 2001, the Congressional Budget Office (CBO) projected under a current law baseline that the federal government would erase its debt in 2006. By 2011, the U.S. government would be $2.3 trillion in the black.

The reality, of course, has turned out to be far different: the U.S. will likely owe $10.4 trillion this year, its largest debt relative to the economy since 1950.

What caused this $12.7 trillion shift?