This is from Mark, the caps are his:
We had these big interconnected undercapitalized things that were mandated by federal policy to keep expanding the amount of paper they bought or backed, which meant inevitably they were going to reach the point where the paper they were backing was too risky, and the GSE’s mandated growth necessarily called for them to issue more paper of their own to do that..And then you had Basel II and its US application that made GSE paper Tier I capital to support maximum loan growth in private sector banks. No wonder credit dried up when the GSEs were taken over in Sept 08. But you never see the Rortys and Mins speak to this perspective. THE GSE’S WERE PROCYCLICAL VECTORS THAT TRANSFORMED HOUSING DEMAND TRENDS INTO CREDIT MARKET TRENDS AND VICE VERSA, FREQUENTLY AMPLIFYING THEM, BUT THEY WERE NOT STRONGLY CAPITALIZED ENOUGH TO ABSORB A TREND REVERSAL.