The Community Reinvestment Act was part of the trigger. It forced (and incented) banks to give loans to subprime borrowers that they couldn't pay off, because, well, they're ******* SUBPRIME BORROWERS, and don't have the brain cells necessary to manage their funds.
So they default, lose their homes, and immediately start sucking at the govt teat. Since they're poor money managers, they welcome the nanny state, and like sitting at home watching Oprah and Springer, eating CheezyPoofs, and basically using tax dollars to subsidize their inactivity. Since they can only afford the essentials (cell phone, cable tv/DVR, fast food, and alcohol), they're not buying "luxury items" and aren't creating jobs with their purchases (like a new house would).
THAT'S WHAT STARTED THE ECONOMIC SLOWDOWN. Making more government-dependent money wasters, and making the workers and wage-earners pay for them.