EXDIMER was posting about the process of banks using mortgages in securitizations the end up aka Mortgage Backed Securities. That is valuable support information and pertinent to the discussion on this iHub WMIH message forum of late.
WaMu loan "portfolio" is completely different. A "portfolio" loan, or an "asset loan" is one (mortgage) that is retained by the bank. It has not been sold via securitization. WMB had $240 billion or so when seized and the reporting by the FDIC-R inception balance sheet and the JPMorgan 2008 annual report disclosures show the clear path these portfolio loans took when sold to JPMorgan Chase.