Forcing Fannie Mae and Freddie Mac to reduce the size of their retained portfolios should not have any impact on demand for mortgage assets, according to one veteran researcher, because there are enough MBS investors to make up for the lost purchasing power of the government-sponsored enterprises. Dwight Jaffee, a finance professor at the University of California at Berkeley, presented his idea of how the secondary market would operate sans Fannie and Freddie during a…