Fannie Mae officials last week said the tough reform bill pending in the Senate could force the government-sponsored enterprise to slash its huge MBS portfolio to as little as $10 billion – about as much as Amsouth Bank holds. Proposed caps on GSE retained portfolios have been the most hotly debated issue in the long-stalled effort to enact stronger regulatory oversight of Fannie Mae, Freddie Mac and the Federal Home Loan Banks. As Congress returned from recess this week, the legislation remains deadlocked in the Senate...