The housing crisis didn't begin with the bankers (who had nothing to do with it), lenders (who had enormous amounts), traders (who had less), or borrowers (who also had enormous amounts.)
It started with the government. The government changed the rules. In order to make loans accessible to anyone it changed the laws to encourage loans going out to people with bad credit. Lenders swept in and started offering loans to people that they knew likely couldn't pay it back, because the government changed regulations so that these people could. The lenders immediately sold these loans to traders, most of whom had no idea what was going on.
Borrowers were taking loans they knew they couldn't pay.
Lenders were giving them, and as someone that sadly spent a year doing operations/marketing at one of these right out of college, I can tell you most were bending rules for this. I didn't see it first hand, as the ops guys ran my company in a constant struggle with sales guys, but the stories we heard from other companies... and the photoshopped documents we got from borrowers to try to support their loans...
Traders were backing and trading these without a clue.
But it all stemmed from the government relaxing regulations stupidly.
Also, I'm ok with people mocking Obama for being owned by corporations as long as they aren't stupid enough to act as if the Republicans aren't even more in debt to corporate overloads. If the Democrats are 99% the Republicans are 105%.