The primary purpose of modeling is to be able to make good decisions. Having spent a decade in CMBS stress testing, in this monograph, I examine credit and default risk, that is, take it apart and deconstruct these concepts and show that defaults are easy to define but difficult to measure, but more importantly default risk cannot be used to determine credit risk. That pre-payers cannot be lumped together with defaulters as they belong to different population demographics. I then reconstruct the credit and default risk models to provide a much better model for forecasting securitized mortgage portfolio defaults. Vasicek is replaced by the Default Covered-Call Model which consists of the Sustainable Cash Flow Line, Lender ’s Default Function and the Borrower ’s Default Function. While the securitized mortgage industry addresses the Dodd-Frank risk-retention from a lender's perspective, from an investor’s perspective, Dodd-Frank is wanting. Therefore, Dodd-Frank is vague and needs much rework.