It all began with a change in the Community Reinvestment Act [CRA] - backed by Clinton, Frank, et al.
Then, they pressured the banks to give loans to unqualified people, and said that Fannie and Freddie would back the loans.
Things then spun out of control and soon, Fannie and Freddie wouldn't accept responsibility for the loans. Thats when the banks came up with the CDO's and CDS's - to spread the risk out.
The head of the Commodity Futures Trading Commission [Brooksley E. Born] under Clinton tried to warn Alan Greenspan et al about the looming mortgage crisis, but was undermined by them when the when the Commission sought to initiate regulation of derivatives. Ultimately, it was the collapse of a specific kind of derivative, the mortgage-backed security years later, that triggered the economic crisis of 2008.
After Bush came into office - his oversight people tried to tell Congress that Fannie and Freddie were built on a house of cards as far as the sub-prime mortgage mess was concerned. Frank, Waters, and a few more libs told them that they were liars and racists. [See video mentioned in this thread].